Demonstrating Protoplasm Continuity

sections with iodine, then dry off the superfluous fluid with blotting-paper, and mount in a single drop of strong sulphuric acid. The cellulose walls and callus will swell; the protoplasm will contract; look carefully over the protoplasmic contents of the sieve-tubes for the points where sieveplates have been ; here it will be found that fine strings of protoplasm, which passed through the sieve -plate, connect the protoplasmic masses on opposite sides of the sieve with one another (cf. Sachs' Textbook, Fig. 47.) By this reaction the continuity of protoplasm through the sieve is demonstrated. It will be noted that the sieve-tubes of Cucurbita, closely resemble those of Helianthus, the sieve-plates being transverse and simple. This is the usual type of sieve-tube to be found in primary phloem of Angio- sperms, and generally in herbaceous stems of the same group. In the secondary phloem of ligneous stems a more complicated type of sieve-tube is found. This will be studied below in the stem of the Lime. ii. Tilia (Lime). I. Cut radial sections of the phloem of a stem of Lime more than three years old. Mount in glycerine and examine with a high power for sieve-tubes. The general arrangement of the phloem is similar to that in STEM. LATICIFEROUS TISSUES. 87 the Elm. The sieves occur on oblique walls facing the radial plane, and are therefore here seen in surface view. Note that they have a similar appearance to those above described, but here three or more sieve- plates occur on each oblique wall. II. Cut tangential sections of the same ; mount as before. The oblique walls are here cut longitudinally ; the sieve-plates are often callous, especially in autumn. Note the form of the segments of sieve-tubes ; it is fundamentally the same as that of the cambium cell, as seen in tangential section. LATICIFEROUS TISSUES. The material for the study of these tissues should be prepared by treatment with alcohol to coagulate the latex. Care should be taken to place the material in alcohol directly it is cut, or at least the cut surfaces should be wetted with alcohol so as to check the flow of latex from them. If the latex be allowed to escape, the laticiferous tissues are emptied, and are then much less easily traced than when they are full. The best method is perhaps to preserve the -whole plant without injury in alcohol, in which case the latex will not be lost at all. i. Laticiferous Vessels. I. Cut tangential sections from the phloem of the root of the Dandelion (Leontodon Taraxacum}, mount in potash and glycerine, and warm ; examine under a low power. 88 PEACTICAL BOTANY. The main constituents of the tissues are parenchymatous cells, with thin walls (phloem-parenchyma) : sieve-tubes are to be met with here and there. The whole mass of tissue is permeated by a ramifying, and profusely anastomosing network of laticiferous vessels. The communication of these tubes with one another is demonstrated by the continuity of their contents (latex), which appear brown and granular. The course of the vessels is mainly longitudinal, while lateral, horizontal branches frequently connect the parallel tubes. With a high power make out more accurately the course of a group of the vessels. II. Cut transverse sections of the same mount in ; glycerine, and examine with a low power. The laticiferous vessels appear circular in transverse section, and have brown contents ; they are distributed in groups, which form more or less regular concentric rings round the central xylem. Note in these sections the presence of sphere crystals of Inulin. In the former section they will have been dissolved by the treatment with potash. Observe that they are formed quite irrespective of the cell-walls, which are often included in them. Treat the sections with iodine solution. They are not definitely stained. Run some potash under the cover slip. They will be gradually dissolved without swelling. The development of tlie laticiferous vessels may be traced by cutting thin longitudinal sections through the cambium of the root of the Dandelion. By careful comparison of such sections it STEM. LATICIFEROUS TISSUES. 89 will be found that they originate from a number of originally separate cells of the cambium, the cavities of which are thrown together by the partial or complete absorption of the walls. Such fusions may appear in the terminal or the lateral walls. ii. Laticiferovs Cells, I. Cut tangential sections of the cortex of Euphorbia splendens (other species will do) just outside the vascular ring, and mount in water, or dilute glycerine. Examine with a low power. Running through the cortical parenchyma will be seen long tubes, with thick cellulose walls and granular contents. These are the laticiferous cells, which differ from the preceding in being developed, not by fusion of originally distinct cells, but by continued apical growth of single cells. Note cases of branching of these cells. Included in the granular contents are starch-grains of peculiar dumb-bell form. Treat sections with iodine solution, and observe the effect on these bodies. II. Cut transverse sections of the same stem, and note the distribution of the laticiferous cells ; they may be recognised by their walls, which are thicker than those of the surrounding tissues, and appear circular in section. III. Separate the whole cortex from a piece of the stem ; boil it in potash for about five minutes, and tease out the long laticiferous cells with needles ; mount, and observe with a low power. They appear as long cylin- drical structures, with thick walls (note striation). Observe occasional branching. They are usually broken at the ends. 90 PRACTICAL BOTANY. LEAF. A. PETIOLE. External Characters. Note in the leaf of the Sun- flower the channelled upper surface, and the insertion on the stem by a broad Pulvinus; in the axil may usually be observed an axillary bud. I. Cut transverse sections of the petiole and mount in glycerine. The details of structure resemble in many respects those of the young stem, from which the petiole differs in the following points : 1. The general outline of the section is semilunar, the concave being the superior (ventral), while the convex is the inferior (dorsal) surface : thus the petiole is dorsiventral whilst the stem is polysymmetrical. (This property extends also to the vascular bundles, of which the xylem is as a rule directed towards the upper surface.) 2. In the presence of numerous Stomata (two guard cells, cf. infra) ; beneath each stoma the collenchyma is replaced by chlorophyll-containing parenchyma with intercellular spaces. Note beneath each stoma the large respiratory cavity. 3. In the number and arrangement of the vascular bundles. In the petiole there are three main bundles, besides several smaller ones (cf. observation of stem with the naked eye, p. 47). 4. In absence of interfascicular cambium, the larger bundles are, for a time at least, open bundles, [i.e. have an active cambium,] while the smaller ones are closed [i.e. have no secondary thickening by cambium.]. SUNFLOWER. LEAF. 91 5. No general bundle-sheath is present, though each bundle is surrounded by a layer of colourless cells without intercellular spaces, which may be regarded as representing the bundle-sheath. B. LAMINA. Bifadal Type. I. Take a piece of the lamina of the leaf of the Sunflower, including the apex : it is important that it should be previously bleached by treatment with alcohol; warm it gently in a mixture of dilute glycerine and potash, and mount in glycerine : examine with a low power, and observe 1. The midrib, with its strongly marked vascular bundle, running up to the apex of the leaf, where it terminates abruptly in a mass of glandular parenchymatous tissue. 2. Lateral branch-bundles passing off from it, and forming a network by frequent anastomoses, while some branches run up into and terminate in the serrate projections of the margin of the lamina in a manner similar to the midrib as above described. 3. Smaller branch-bundles, which sometimes end blindly in the parenchyma filling the meshes of the network. II. Cut off a small square piece of the lamina of a leaf of Heliantlius, including one of the main ribs or nerves, and imbed in cocoa-butter or paraffin (cf. directions, p. 4), so that the rib shall be perpendicular. Cut transverse sections, and mount in glycerine. If cocoa-butter has been used, it may be dissolved off the sections with ether or chloroform. 92 PEACTICAL BOTANY. Good sections may be obtained by holding the piece of lamina between slices of carrot, or pith ; or by folding the whole lamina repeatedly, and cutting sections from the whole mass. In these cases, though the chlorophyll appears of a better colour, the sections not having been treated with a solvent (alcohol), still the sections are infested with air bubbles, which may be partially removed by leaving the sections for some minutes in water ; they may be completely removed (though the chlorophyll would be dissolved) by treatment with alcohol. Difficulty will often be found in obtaining good preparations of the above ; all the important points may be more easily observed in the Cherry Laurel. Note with a low power 1. The general outline of the section, which is irregular and undulating, though it is in the main of uniform breadth. At the point corresponding to the main nerve the section widens out, the nerve appearing semilunar, as in the petiole. The convex side is the inferior (dorsal), and the concave the superior (ventral) surface. 2. That the margins of the sections (i.e. the superior and inferior surfaces of the leaf), are studded with projecting multicellular hairs. 3. That the arrangement of the tissues in the large nerve resembles that in the petiole, though less complicated. Thus it often has but one large central bundle, with smaller lateral ones. The position of the xylem and phloem relatively to the whole leaf corresponds to that in the petiole, i.e. xylem towards the upper surface, phloem towards the lower. Occasionally some of the smaller bundles in the vein are inverted, showing an approach to the arrangement of bundles in the polysymmetrical stem. 4. Smaller veins, with correspondingly reduced SUNFLOWER. LEAF. 93 vascular bundles, are found scattered through the thinner part of the section. Next examine the thinner part of the section, or the Lamina proper with a high power, and, starting the study of the several tissues from the upper surface. Note successively the following tissues : 1. Upper layer of Epidermis, continuous with that covering the nerve ; it is a single layer of cells, covered externally by Cuticle, and with the same characters as that of the stem (cf. p. 51). It bears numerous multicellular hairs (already studied in con- nection with the apical bud). Stomata occur in considerable numbers (cf. infra). Beneath this layer lie- 2. Thin-walled, oblong cells, with copious protoplasm, and chlorophyll grains ; they are arranged with the longer axis perpendicular to the outer surface, and form two layers; this tissue, from the form and arrangement of the cells, is called the Palisade parenchyma ; below it is A 3. mass of parenchymatous cells of irregular form, with large intercellular spaces ; in general characters they resemble (2) ; this is the Spongy parenchyma. (2) and (3) are together included under the general term Mesophyll. Embedded between (2) and (3) are 4. Numerous smaller vascular bundles (nerves) of various size, often reduced to a single pitted or spiral tracheide, surrounded by a colourless sheath of paren- chyma similar to those in the petiole. The course of these bundles is diverse, since they form the reticulate system of veins ; they may thus be seen in the sections 94 PKACTICAL BOTANY. to have been cut transversely, obliquely, or longitu- dinally. A 5. second layer of epidermis bounds the section on the lower side it has the same characters as the ; upper layer, but stomata are more frequent. Note the large respiratory cavity, and two small guard cells. Hairs as before seen on the upper surface. Note the mucilaginous walls of these hairs. Since the leaf of Heliantlius is not a universal type, it would be well to study also the structure of other types, for instance the coriaceous leaves of the Cherry Laurel (Prunus Lauro-Cerasus), and the cylindrical leaves of the Stonecrop (Sedum acre). Special structural peculiarities are to be observed in the leaves of other plants ; for instance, an epidermis consisting of more than a single layer of cells, e.g. in leaves of Ficus, Piperacece, Begoniacem, &c. ; Cystoliths in the cells of the epidermis, e.g. FicuSj Urtica, &c. ; glandular structures, e.g. in Ruta, Psoralea, &c., &c. III. Taking that of the Cherry Laurel sections maybe prepared as above directed for the Sunflower, and be mounted in dilute glycerine. Starting from the upper surface, observe successively the following tissues 1. Epidermis, a single even layer of cells, with thick walls, and colourless protoplasmic contents ; no hairs or stomata are to be seen ; the lateral walls are pitted ; the outer wall is differentiated into a. Cuticle, a continuous, well-defined layer, covering the whole epidermis externally. CHERRY LAUREL. LEAF. 95 1. Cuticularised layers, of granular appearance; they are intermediate in properties between cuticle and true cellulose. c. The cellulose layer, which abuts on the cavity of the cell. i. These several layers may be readily distinguished in sections treated with fuchsin. a and b stain much more deeply than c. ii. Treat sections with concentrated sulphuric acid, a retains a sharp contour ; the rest of the wall swells, and loses distinct- ness of outline. iii. Boil some sections for a long time with strong potash, a and the cuticular granules of b will he dissolved, while c and the cellulose matrix of b will remain. 2. The Palisade parenchyma, composed of thin- walled, oblong, closely-packed cells, with their longer axes perpendicular to the surface of the leaf; the cells are somewhat irregularly arranged in three layers; observe nuclei and chlorophyll grains ; here and there are cells with but little protoplasm (Idioblasts) in which is inclosed a large crystal. Passing towards the lower surface of the leaf, this tissue merges gradu- ally into 3. The Spongy parenchyma, the cells of which resemble those of (2) in general characters ; but their shape is various, and large intercellular spaces occur. Idioblasts with crystals are scattered here and there. Imbedded between (2) and (3) are 4. Vascular bundles of various size the direction ; in which these run is not uniform (cf. reticulate venation of leaf) ; the positions of xylem and phloem with regard to the whole leaf are the same as in the Sunflower ; the bundles are surrounded by a continuous 96 PRACTICAL BOTANY. colourless sheath of cells without intercellular spaces. At the lower limit of the section lies 5. The lower Epidermis, which resembles (1) in general character; but differs in having numerous Stomata. Note the appearance presented where the two Guard cells of a stoma have been cut transversely, and observe carefully a. The form and position of the two guard cells. I. The cavity or intercellular space between them (the Pore) ; this leads into c. The large, intercellular space (Respiratory cavity) in the tissue beneath the stoma. d. In the sections stained with Schulze's solution or with fuchsin, note the continuity of the cuticle round the guard cells, into the pore of the stoma. IV. Cut tangential sections from the upper and under surfaces of the leaf, and mount separately with the external surface in both cases uppermost. The cells of the upper epidermis are tabular, with sinuous outline the ; surface has a granular appear- ance (explained by the granular cuticularised layers observed in transverse sections) ; the lateral walls are pitted; contents colourless; no stomata. The cells of the lower epidermis are similar to the above ; but stomata are numerous ; they have no definite arrangement. Note the two sausage-shaped nucleated guard cells, inclosing the pore ; they contain chlorophyll. (For development of stomata, cf. Hyacinth, p. 117.) V. No Subsidiary cells are found in the Cherry Laurel. The leaves hitherto studied are of the bifa- cial type, i.e. the difference of the upper and lower STONECROP. LEAF. 97 surfaces is recognisable by a different arrangement of the tissues at or beneath those surfaces. It may be noted that the leaf of the Cherry Laurel is of a more pronounced bifacial type than that of the Sunflower, since in the latter case stomata arc found on both surfaces, while in the former they occur only on the lower surface. Centric Type. We have now to study leaves of the centric type, i.e. such as have their tissues arranged symmetrically. It is usually in succulent leaves that this arrangement is found, and they are of an approximately cylindrical form. As an example we may take the leaf of Sedum acre (the common Stonecrop). VI. Cut transverse sections of the leaf of the Stone- crop ; mount in water, or dilute glycerine, and observe that the outline of the section is even and oval; the arrangement of tissues is concentric, and is uniform all round, so that beginning at any point of the periphery and passing inwards we encounter 1. The Epidermis, a single layer of cells of variable size and shape, with well-defined Cuticle, and Stomata, the guard cells of which are much smaller than the epidermal cells. 2. Chlorophyll-containing mesophyll, which is not differentiated into palisade, and spongy parenchyma ; this tissue forms the great mass of the leaf; intercellular spaces occur; the cells are thin-walled, with a protoplasmic sac, in which are imbedded chlorophyll grains, and there is large central vacuole. Observe the chlorophyll grains undergoing division. Embedded in this tissue lie centrally H 98 PKACTICAL BOTANY. 3. Vascular bundles of small size : their number varies from 3 to 5. Strip off a piece of epidermis from the leaf of Sedum acre, and mount in water. Note : 1. The Epidermal cells with sinuous outline, nucleated : with no chlorophyll. 2. The Stomata with two guard cells surrounding the pore as in the Cherry Laurel. Surrounding these are : 3. Three Subsidiary cells, which differ in size and shape from the ordinary epidermal cells, and are arranged in definite order round each stoma. Beneath the epidermis will usually be found cells of the mesophyll, with thin walls, large vacuole and protoplasmic sac, in which are embedded chlorophyll grains. By making similar preparations from successively younger leaves the development of the stoma and subsidiary cells may be traced as follows. From, one of the similar epidermal cells a smaller cell is cut off, from this are successively cut off the three subsidiary cells, the remaining cell is the mother-cell of the stoma, which divides to form the two guard cells. On the leaves of many plants, stomata of large size are to be found situated above the free endings of the vascular bundles of the lamina, and especially at the tips of the teeth : these are often incapable of closing, and are concerned in the secretion of water : hence they are called water-stomata. In certain cases (Saxifragacece and Crassulacece) a mass of cells of the mesophyll is specially differentiated as glandular tissue (the water-gland) ; it is connected with the termination of a vascular bundle. SCAELET EUNNER. ROOT. 99. ROOT. Observations with the Naked Eye. Germinate seeds of Phaseolus multiflorus (the ScarletRunner) in wet sawdust, or pure vegetable mould, till the primary root has attained a length of six to eight inches. Note with the naked eye 1. The Seed, from which the testa can easily be removed, disclosing 2. The two fleshy Cotyledons (no endosperm is present) : between these 3. The Plumule, which develops early as a stem, bearing foliage leaves. 4. Below the cotyledons a short Hypocotyledonary Stem, not clearly marked off externally, except by colour, from 5. The Primary root, on the upper part of which are 6. Numerous secondary, or Lateral roots. These are formed in acropetal order, and are arranged in regular longitudinal rows, usually four in number. On the youngest part of the primary root (i.e. within three inches or more of the apex) no lateral roots are to be seen. Observe that particles of the sawdust, &c., adhere to the older parts of the roots, while the younger apical parts come out of the soil quite clean. Microscopic Observations. Harden the roots in alcohol for two or three days or more. I. Cut transverse sections of the primary root at a point nearer the apex than the youngest lateral roots, H2 100 PRACTICAL BOTANY. i.e. about two inches from the end. Treat with dilute potash for about ten minutes, and mount in glycerine. N. B. It will be found convenient to hold the roots in pith, or otherwise to imbed, while cutting the sections. Observe the following tissues : 1. At the centre of the circular section is a mass of Parenchymatous Pith. At the periphery of this are 2. Four radiating groups of elements of the Primary Xylem, which are the most strongly marked tissues of the young root. They have dark lignified walls (test with Schulze's solution or aniline sulphate), and resemble the primary xylem of the stem. Note fresh elements in course of formation at their central limit. The development is thus centripetal. Alternating with these may be seen 3. Four groups of Primary Phloem, which are not as yet very well marked. These several groups of elements are separated laterally from one another by bands of parenchyma. At the periphery of the central cylinder thus built up is 4. The Pericambium or phloem-sheath, consisting of thin-walled cells, arranged in an undulating band, which is a single layer of cells in thickness, peripherally to the phloem, but opposite the xylem it consists of two to three layers of cells. 5. Immediately outside this is the Bundle-sheath, consisting of a single layer of cells, having the characteristic dark dot on their radial walls. Then follows 6. The parenchymatous Cortex, a thick band of tissue, with intercellular spaces, and 7. The Epidermis, a single layer, not well marked. SCARLET RUNNER. Single cells will be seen to have grown out perpendicu- larly to the surface as root-hairs. II. Cut sections successively at older points in the same root,- and observe the mode of origin of the lateral roots, noting more especially the following facts : a. The lateral roots arise opposite the groups of primary xylem : this explains their arrangement in four rows as above observed with the naked eye. Z>. The pericambium, bundle-sheath, and a small portion of the cortex, all take part in their formation. c. In the older lateral roots it may be seen that their vascular system is continuous with that of the main root. This mode of origin of the lateral roots is the rule in the plants with apical meristem, arranged according to Type II. (cf. infra, p. 104). In the plants whose root-apex follows Type I. the lateral roots are mainly, or even entirely, derived from the pericambium. III. Cut transverse sections of the root, six inches or more from the apex, taking care to avoid the lateral roots : treat as before. The general arrangement of tissues is the same as has been above described, though there has been increase in bulk, and the xylem and phloem, being now more fully developed, are more easily recognised. Observe especially that the parenchyma, lying centrally to the phloem, has begun to divide repeatedly by tangential walls : in fact, four cambium bands are thus formed, from which is derived the secondary thickening of the root. IV. Cat transverse sections of an old root of the Scarlet-Runner, and treat as before. Observe 1. Centrally a parenchymatous Pith, relatively to which PRACTICAL BOTANY. 2. The four Primary Xylem groups retain their original position. 3. Four large wedges of Secondary Xylem have originated internally from the four cambium zones. These are separated from one another laterally by 4. Four broad Parenchymatous rays, which lie on the same radii as the primary xylem. Outside the xylem is 5. The Cambium, having similar characters to that of the stem, and giving rise peripherally to 6. Secondary Phloem. Note if possible 7. The four groups of Primary Phloem now sepa- rated from the primary xylem, but still on radii alternating with the latter. The section is bounded by 8. Cork with a Cork-cambium. Apex of the Root. Type I. Cut thin median longitudinal sections of the apex of the radicle of the straight embryo of Helianthus. [The arrangement of the meristem at the apex of the radicle of the embryo is similar to that of the apex of the growing root, and the former is chosen in this case as it is much easier to make preparations from it than from the growing root. The sections are of little use unless they are accurately median.] Treat the sections with potash for ten minutes or more : wash with water, and mount in glycerine : examine with a low power, and observe that 1. The mass of tissue is composed of thin-walled cells, arranged regularly in longitudinal rows. APEX OF THE ROOT. 103 2. That these rows of cells converge towards a point at some distance below the external apex of the root. This is the punctum vegetationis. 3. Note the Procambium-cylinder, or formative tissue of the vascular bundles, which pursues a longitudinal course up the centre of the root. Examine with' a high power : and observe that 1. At some distance from the apex a definite layer of Epidermis covers the root externally. Follow this towards the apex : at some short distance from it this single layer splits into two : the inner is the Dermatogen, or formative layer of the epidermis : the outer is the outermost layer of the Calyptra, or root-cap. Following the dermatogen further inwards, it will be seen to split again several times in succession : the dermatogen may be traced as a continuous layer covering the inner tissues. The layers thus thrown off externally from the dermatogen form collectively the Root-cap, or Calyptra. We have in this case a common formative layer for epidermis and root-cap (cf. root of Maize, p. 120.). 2. Between the procambium and epidermis lies a broad band of formative tissue of the cortex, or Periblem : follow this to the punctum vegetationis : it is also a distinct continuous band, though reduced to a single layer of cells at the apex. 3. The Plerome, or central procambium cylinder, may also be traced as distinct up to the apical point. This type of arrangement of tissues of the meristem may then be expressed thus : Calyptrogen \ a single layer of cells, i.e. epidermis and Dermatogen j root-cap have a common origin. 104 PEACTICAL BOTANY. Periblem, distinct from the rest. Plerome, distinct. To this type belong most of the Dicotyledons. The work may be equally well done on Linum usitatissimum, or Polygonum Fagopyrum. Type II. Prepare median longitudinal sections of the apex of the radicle of Phaseolus multiflorus (the Scarlet-Runner), and treat as the above. Examine with a. low power and make out 1. Calyptra (Eoot-cap). 2. Epidermis. 3. Periblem. 4. Plerome, forming the procambium and pith. But here all the different tissue-systems will be found to originate from a general meristem, the original formative tissue of none of them being distinct from that of the others. This type may be expressed shortly, thus : Calyptrogen \ Dermatogen All ( united in a general, undifferen- Periblem ( tiated mass of meristem. Plerome / As alternative plants of the same type, may be named Cucurbiia and Pisum. VEGETATIVE ORGANS. (B.) MONOCOTY- LEDONS. EMBEYO AND GERMINATION. Soak fruits of the Maize (Zea Mais) in water for several hours. N.B. The fruit is a caryopsis, and results from the develop- MAIZE. GERMINATION. 105 ment of both ovule and ovary ; its form is compressed conical, the apex of the cone being the basal point of attachment of the fruit. I. Strip off the external coat of the fruit: this represents both the wall of the ovary and the integument of the ovule. If sections be cut, these two layers may be distinguished from one another, under a low power. Distinguish in the body of the fruit which remains A 1. lateral, smaller, white portion: this is the Embryo. A 2. larger yellow part, which forms the mass of the fruit : this is the Endosperm. greater Separate the embryo from the rest, and note its shape. II. Cut longitudinal sections of the fruit, so as to include the axis of the embryo : mount in glycerine, and examine with a low power ; observe i. The coat of the fruit, consisting of two layers. Note at the apex of the fruit the remnant of the Style, and at the base the attachment. ii. The Endosperm, consisting of thin-walled parenchyma; the cells contain polygonal starch grains, embedded in a matrix of protoplasm : in the peripheral yellower portion of the endosperm the starch grains are more closely packed than in the central whiter portion. iii. The Embryo, which is in close apposition to the endosperm : the part which is in contact with it is the Scutellum (cotyledon); it extends over the whole surface of contact, and almost completely surrounds the 106 PRACTICAL BOTANY. body of the embryo itself. Note (a) the central attachment of the scutellum to the body of the embryo ; (fy the vascular bundles, which form a connection through it ; (c) the Epithelium of peculiar structure, which faces the endosperm. The body of the embryo consists of a. An Apical bud, with several sheathing leaves, which surround the apical cone. A b. Radicle, having similar arrangement of the meristem to that of the older root (cf. infra.). Outside the radicle, and continuous with the root-cap, is a root-sheath or Coleorhiza, the existence of which shows the endogenous origin of the radicle. III. Cut sections of the endosperm, and treat with solution of iodine. Note the polygonal starch grains (blue), and the protoplasmic matrix (brown). Germination. I. Compare plants which have been germinated for different periods : the following facts in the history of germination may be observed : 1. The fruit swells. 2. The outer coat ruptures opposite the apex of the radicle, which soon protrudes aod bursts through the coleorhiza also, which appears as an irregular ring round the young root. 3. The rupture of the coat extends upwards to the point opposite the apical bud, which also emerges. 4. The root elongates, and forms lateral roots : other lateral roots (usually two) appear above the insertion of the scutellum : these soon equal the primary root in length. Hence there is no well marked tap root. 5. Leaves of the plumule unfold, and gradually turn green. MAIZE. STEM. 107 IV. From a young plant with leaves about three inches long cut longitudinal sections, as above : mount in water, and irrigate with solution of iodine. Observe 1. That in the neighbourhood of the surface of the scutellum the starch grains are in course of demolition, and that the central part of each is first attacked. 2. That no starch grains are to be seen in the epithelium of the scutellum. STEM. HERBACEOUS TYPE. I. Cut transverse sections of an internode of a well-grown stem of Zea Mais ; mount in water. N.B. Fresh material may be used, but stems preserved in alcohol are preferable. When fresh, the tissues are crowded with air bubbles. The sections should be cut from the upper part of one of the lower internodes, otherwise the vascular bundles may- be found to be imperfectly developed. Examine with a low power, and, beginning the study of the tissues at the periphery of the section, observe A a. single layer of Epidermis, having the usual characters : immediately below this are b. Irregular groups of Sclerenchyma with thick lignified walls : internally lies A c. mass of Parenchyma, which forms the ground- work of the whole section : embedded in this are d. Numerous Vascular bundles : note that they are smaller, but more numerous near the periphery than at the centre ; also that the position of the parts of the bundles relatively to the centre of the section is uniform. 108 PKACTICAL BOTANY. Treat a section with Schulze's solution : put on a high power, and examine in detail the several tissues above-named. a. The Epidermis appears as a definite layer of cells of unequal size, without intercellular spaces. Note a well-marked Cuticle (brown). Here and there may be found Stomata, with two small guard- cells and two subsidiary cells (the structure and development of the stomata will be studied in the leaf; p. 116). b. The Sclerenchyma consists of cells with thick, highly refractive walls, which stain yellowish brown with Schulze's solution (lignified). Note that it does not occur immediately below the stomata, but, as usual, there is there an intercellular space (respiratory cavity). c. The Parenchyma consists of cells with thin cellulose walls (blue with Schulze's solution). At the angles where the cell-walls meet are intercellular spaces. The external layers have abundant protoplasm with chlorophyll-grains. These are less frequent in the inner layers, while in the central parenchyma the protoplasm is hardly appreciable. d. For the minute study of the Vascular bundles select one of the largest central bundles. The section must be thin. The most prominent elements in the bundle are i. Four large Vessels of the Xylem, arranged like a V, with the angle towards the centre of the stem : of these the two smaller are developed first. Compare sections of young stems. In many Monocotyledons the arrangement of the constituents MAIZE. STEM. 109 V of the xylem in the form of a is much more plain than here, e.g., Asparagus. In other cases (e.g. Calamus) this arrangement is not to be seen. The vessel nearest the centre of the stem has annular thickening : in old stems it is partially surrounded by an intercellular space, while the rings often become detached, in "which case the vessel is not easily seen in transverse sections. Next this is a spiral vessel : the remaining two have thinner walls with pitted marking, and large cavity. Surrounding the pitted vessels, and between them, are A ii. number of Tracheides with pitted lignified walls, and no cell-contents. Surrounding the inter- cellular space above described is A iii. group of parenchymatous cells with thin cellulose walls. These may be regarded as Xylem Parenchyma. The Phloem portion of the bundle lies between the limbs of the V-shaped xylem, and is easily recognised by the thin cellulose walls characteristic of Soft bast. It consists of iv. Elements with large cavities, in which transverse septa (sieve-plates) often occur. These are Sievetubes. v. Smaller cells (cambiform) between the sieve- tubes. Surrounding the above tissues of the xylem and phloem is a Sheath of sclerenchyma. Transitional forms may be found on its internal side, between sclerenchyma, and certain of the constituents of the bundle. 110 PRACTICAL BOTANY. II. Cut longitudinal sections of the same, treat as before, and observe a. The Epidermis composed of oblong cells. &. The prosenchymatous cells of the Sclerenchyma. c. The ground parenchyma with roundish cells. d. The Vascular bundles pursuing a longitudinal course parallel to one another, without lateral fusion. In the Xylem observe i. The annular, spiral, and pitted vessels, and note, especially in the latter, the clearly-marked joints, pointing to their origin from a succession of cells. ii. The pitted Tracheides. iii. The thin-walled Parenchyma. And in the Phloem (which is easily recognised by its cellulose walls, blue with Schulze's solution) distinguish iv. The Sieve-tubes, which have a wide cavity, intercepted here and there by transverse sieves. !N .B. If it be found difficult to distinguish the sieve- plates, a fresh section may be treated with potash ; the character of the sieve-plate is then more easily seen. v. The Cambiform cells, which are narrow and pa renchymatous. Note the prosenchymatous constituents of the sheath of Sclerenchyma, and observe transitional forms between these and the pitted Tracheides (ii.) with square ends, which belong to the xylem. III. Cut successive, thick transverse sections through a node : treat them with strong potash [or better, soak them for twenty-four hours or more in dilute potash] ; mount in glycerine, and examine with a low power. MAIZE. STEM. Ill Observe that the vascular bundles here form a dense plexus, in which may be recognised 1. Branching, and anastomosis of the bundles of the main axis with one another, at the base of the internode. 2. Entry of the bundle-system of the leaf-trace, and of its axillary bud, into the main axis, in which the bundles at first pursue an irregular horizontal course. 3. Anastomosis of these bundles with those of the main axis. The result is a thorough intercommunication of the several systems of bundles, one with another, at the node. This modification of the type of bundle arrangement characteristic of the Monocotyledons is the rule in those of the group which have long internodes. Observe that the structure of the individual bundles at the node differs from that in the internode, the change depending upon 1. The sheath of sclerenchyma being relatively larger. 2. The irregularities of vascular arrangement result- ing from the fusion of bundles. IV. Cut longitudinal sections through a node in planes parallel to the median plane of the leaf and axillary bud : treat as above, and observe 1. The branching and fusion of the longitudinal bundles of the internode at the node. 2. The entry, horizontal course, and fusions of the bundle system of leaf, and axillary bud. Note that the plexus of bundles at the node does not extend far in a perpendicular direction. V. Apex of stem, to show the fundamental arrangement of the vascular system. Cut median longitudinal sections through the apex of a young plant of Maize, 112 PKACTICAL BOTANY. or of a foliage branch of an old plant : treat with strong potash [or better, with dilute potash for twenty-four hours] : examine with a low power, and observe, if the section be median 1. The Apical cone (punctum vegetationis). 2. Leaves, in successive stages of development, seated laterally. 3. In the older leaves, Vascular bundles, which enter the stem. On following the course of these vascular bundles it will be seen that on entering the stem they proceed at first towards the centre : before reaching it they curve downwards, and finally turning again outwards they We approach the periphery of the stem. thus see that in young stems of Maize the course of the bundles cor- responds to the Palm-type, though as the stem grows older, and the internodes develop, the correspondence is less obvious, by reason (1) of the almost straight course pursued by the bundles in the internode, and (2) the complications which arise at the node. STEM. ARBOREOUS TYPE. I. Examine preparations of the old stem of Yucca or Dracaena, in which the thin-walled parenchyma has been allowed to rot away, while the vascular bundles remain. On comparing transverse and longitudinal sections of such stems, it may be seen, with the naked eye 1. That the central Primary bundles are isolated, and that the course of each bundle may be traced as starting from below at the periphery of the stem, then STEM. ARBOKEOUS TYPE. 113 curving towards the centre as it ascends, and finally turning outwards, and passing into a leaf. These are therefore common bundles. 2. That the peripheral mass of secondary bundles increases in thickness towards the base of the stem, and has no direct connection with the leaves. These bundles are therefore cauline. II. Cut transverse sections of the stem of Draccena at a point one foot or more from the apex, and mount in glycerine. Examine with a low power, and ob- serve A 1. well-marked Epidermis. Beneath this A 2. band of Cork (cf. Elm). 3. A broad belt of Cortical parenchyma, many cells of which contain crystals (Raphides &c.) Here and there a vascular bundle will be seen in the cortex, these are bundles of the leaf-trace, passing inwards from the leaves. 4. At the inner limit of this is an actively dividing Meristematic ring, which gives rise internally to new vascular bundles, and externally to fresh cortical cells. The new bundles thus formed are cauline (i.e. have no direct connection with the leaves), and are embedded in lignified ground tissue. These together form a dense ring. 5. Centrally, an arrangement of thin-walled Paren- chyma and Vascular bundles, similar to that in the internode of Maize. Note the passage of these central bundles outwards to the bases of the leaves. They are common bundles. Note also the mode of formation of the cauline bundles (cf. Hippuris). 114 PRACTICAL BOTANY. Transverse sections should also be cut immediately below the apical tuft of leaves. Here the secondary thickening will not have begun, the arrangement of tissues resembling, in all essential points, that in the internode of the Maize. LEAF. Note the phyllotaxis in the Maize ; the leaf is sessile, and sheathing in its lower half, with a ligule at the apex of the sheath ; lamina, form lanceolate, margin entire, ciliate, midrib well marked ; venation parallel ; upper surface hirsute ; lower glabrous. I. Cut transverse sections of the lamina mount in ; water, or dilute glycerine. Other sections may be treated with alcohol to expel the air bubbles (the chlorophyll will, at the same time, be dissolved out), and be mounted in Schulze's solution, and kept for comparison with the above. Examine with a low power. The section presents a sinuous outline, corresponding to a certain extent to the arrangement of the main vascular bundles. At the mid-rib the section widens out. tissues : Note the following arrangement of 1. Covering both surfaces of the leaf is an Epidermis, resembling that of the stem, but bearing hairs of various form, mostly simple, conical. The largest of them are surrounded at the base by an outgrowth of the neighbouring epidermal cells. Note the Stomata on both surfaces, with small guard cells, surrounded by two subsidiary cells (cf. infra). 2. Vascular Bundles of various size, which, in the MAIZE. LEAF. 115 thinner part of the lamina, lie in a median position between the two epidermal layers. The largest of these correspond in structure to those of the internode, the smaller ones are reduced forms of the same type. Note that the spiral and annular vessels (i.e. protoxylem) are nearer the upper surface of the leaf. Between the epidermis on either side, and the larger bundles, are masses of Sclerenchyma, which, together with the bundles, form complete bridges of rigid tissue between the two epidermal layers. 3. The spaces between the tissues, hitherto con- sidered, are filled with parenchyma (Mesophyll), which may either be (a), green (containing chlorophyll) ; or (&), colourless (without chlorophyll). a. The green chlorophyll- containing parenchyma fills up the greater part of the space ; intercellular spaces occur in it. I. The colourless parenchyma occurs (i.), as a sheath, without intercellular spaces, surrounding each bundle (bundle-sheath) ; (ii.) as groups of cells immediately below the epidermis ; these are more common towards the central part of the leaf. At the mid-rib this tissue forms the bulk of the structure. II. Cut transverse sections of the leaf-sheath, and treat as the above. Compare the arrangement of tissues with that of the lamina, and of the stem. Note that colourless parenchyma preponderates. III. Treat a piece of the thin peripheral part of a leaf (which has been previously bleached in alcohol) with potash till it is transparent ; mount in glycerine, and examine under a low power. Observe 1. The parallel course of the Bundles. I2 116 PBACTICAL BOTANY. 2. Their frequent lateral fusion, by means of small branch bundles. 3. The absence of Stomata above the vascular bundles, and their arrangement in rows in the spaces between them. 4. The various forms of Hair; and especially the conical unicellular hairs, which give the ciliate character to the margin of the leaf. IV. Cut thin tangential sections from the under surface of the lamina, so as to remove, if possible, only the epidermis. Treat with potash, and mount in glycerine. Observe 1. The ordinary cells of the Epidermis of oblong form, and with sinuous outline. 2. Short cells between the ends of these, which often project perpendicularly to the surface as Hairs of various form. 3. The Stomata holding the same position as (2) relatively to the oblong epidermal cells. Observe with a high power the structure of the stomata. They consist of a. Two narrow guard-cells, which inclose the pore. I. Two triangular subsidiary cells, which com- pletely surround the convex side of the guard-cells. Compare this view of the storna with the same structure as seen in transverse sections of the lamina. V. Cut tangential sections of the upper surface of the lamina. (1). Mount some, and examine them under a low power. (2). Treat others with nitric acid; dry them, and ignite on platinum foil over a spirit lamp. Mount the ash in water, and examine under a low power. The structure will resemble that of (1). MAIZE. LEAF. 117 Treat with acetic acid no evolution of gas. Treat with nitric acid it is not dissolved. The residue is a silica-skeleton of the epidermal tissues. VI. Development of Stomata. Take a young leaf from a bulb of Hyacinthus orientalis in which the leaves have not yet protruded more than about one inch from the apex of the bulb. Strip off pieces of the epi- dermis (or cut tangential sections at successive points) starting from the apex, and proceeding to the very base. Mount in glycerine, and examine under a high power. i. Starting at the basal part, cell-division will be found to be proceeding actively in the epidermal tissue ; the walls are thin, and protoplasm copious. The epidermis consists of a. Larger oblong cells. b. Short, nearly square cells. The cells are arranged in regular longitudinal rows. ii. At a short distance from the base, the difference in size of (#) and (5) increases ; some of the square cells may be seen to be divided by a thin longitudinal wall, into two equal halves (guard-cells of the stoma). iii. Further up again, this division wall may be seen to be thicker at its central part, while the whole outline of the pair of guard-cells tends to become circular. iv. Again further up, the division wall will be seen to have split, so that a channel is formed between the guard-cells into the internal tissues of the leaf. This channel is the pore of the stoma. v. Near the apex of the leaf the mature stomata may be seen of circular outline ; their guard-cells are sausage- 118 PKACTICAL BOTANY. shaped, and surround the nearly circular pore. cells of the epidermis remain ohlong as before. The It will be seen that; the stoma of Hyacinthus is of simpler structure than that of the Maize. It is more difficult to trace the development of the latter ; but it may be done in the same way in a foliage bud. The main point of difference is that after the mother-cell of the stoma has divided to form the two guard-cells, two other cells are cut off from the neighbouring epidermal cells (subsidiary cells). These lie parallel to the guard-cells. Further, the epidermis of the Maize is complicated by short cells, which appear in irregular groups among the ordinary epidermal cells. This is a common character among the Grasses. BOOT. 1. Cut transverse sections of the root of Hyacin- thus orientalis. (N.B. An old root must be taken, and the sections should be cut as far as possible from the apex). Treat them with potash, and mount in glycerine. Starting from the outside, note succes- sively ' 1. An Epidermis, not well marked. Note here and there cells, which have grown out perpendicular to the surface as root-hairs. A 2. thick band of Cortical parenchyma, consist- ing of rounded cells with intercellular spaces ; in old roots the outer layers of this tissue become disorganised and distorted. The inmost layer of this tissue differs in structure from the rest, and is called 3. The Bundle-sheath : the radial walls of this layer present the characteristic appearance of a black dot, and are cuticularised. Within this is A 4. layer of thin-walled cells (the Phloem-sheath or pericambium), which immediately surrounds HYACINTH. KOOT. 119 5. The central Vascular cylinder. This consists of groups of tissue of two sorts. A. Xylem-tissues, easily recognised by their dark lignified walls. They are arranged in a series of groups of indefinite number, which abut externally on the pericambium, and extend inwards, till they meet internally, and form a central mass. The chief con- stituents are vessels of various form. As may be seen in transverse sections of young roots, the smaller peripheral members of each group are formed first (protoxylem), and have spiral thickening ; then successively the larger vessels towards the centre. Between the peripheral groups of the xylem, and alternating regularly with them may be seen B. The Phloem-tissues, which are groups of ele- ments with small cavity, and bright cellulose walls. II. Cut radial longitudinal sections of the same root : treat in the same way, and observe the several tissues above described. The whole root will be seen to be composed of similar elements to those found in the stem. Transverse sections should also be made of the root of the Maize. The main features of the section are the same, though the structure differs in several minor points from that of the root of Hyacinth. Thus, in the Maize root there is a parenchymatous pith, and the xylem abuts directly on the bundle-sheath. In these sections may be found the point of junction of lateral roots with the main root. It may be seen that the former originate from the pericambium of the main root, and that they break through the bundle-sheath, cortical tissue, and epidermis ; also that their vascular tissue is continuous with that of the main root ; the activity which produces them begins opposite a phloem-mass of the main root, and not opposite a xylem-mass, 120 PKACTICAL BOTANY. as is usually the case (cf. Dicotyledons). This is to be connected with the fact that the xylem-groups in the Maize (and in most Grasses) abut directly on the bundle-sheath. Apex (punctum vegctationis). It is not easy to cut longitudinal sections of the apex of an ordinary fully developed root without embedding. The arrangement of the meristematic tissues is, how- ever, the same in young as in old roots ; it is therefore more convenient, and quite as successful, to cut longi- tudinal sections of the apex of the young lateral roots, which are to be found growing horizontally out of the nodes of the Maize plant. Or, if fitting material for this be not at hand, longitudinal sections may be made of the radicle of the embryo, in seeds which have been previously soaked for several hours in water. Adopting one of the above methods, cut longitudinal median sections of the apex of the root. Treat them for ten minutes with dilute potash : neutralise with acetic acid, and mount in glycerine. N.B. The section must be accurately longitudinal and median, i.e. the section must include the organic axis of the root, around which the several tissues are symmetrically arranged. In a median section the following arrangement of tissues will be visible. A 1. central mass of tissue, clearly defined laterally, and rounded off at its apex, which is at some distance below the external apex of the root : this is the Plerome cylinder. If this tissue be traced back into the older part of the root it will be found that its central part is continuous with the parenchymatous MAIZE. APEX OF ROOT. 121 pith, while its peripheral part develops into the vascular ring. Note rows of larger cells, which may be traced back as continuous with vessels of the xylem. In the central portion of the plerome are intercellular spaces, which appear black in sections from fresh material, being filled with air. 2. Surrounding the plerome is a broad band of tissue with intercellular spaces, which appear as above. This is the Periblem, which is the formative tissue of the cortex. 3. Outside this is a single layer of cells somewhat elongated radially, and with a thick outer wall : this is the Dermatogen or formative tissue of the epidermis. If the section be accurately median it will be possible to trace (2) and (3) upwards, till, immediately above the apex of the plerome, they merge into a single layer of cells : thus the formative tissue from which the epidermis and cortex are derived, is represented at the apex by a single layer of cells. 4. Outside the dermatogen, at the apex of the root will be found another formative tissue, the cells of which divide parallel to the surface of the dermatogen : this is the Calyptrogen layer, which is formative of the tissues of the Root-cap. The latter appears as a mass of parenchyma, covering the whole apex of the root : the outer cells of it will be seen to be undergoing disorganisation, and mucilaginous degeneration of the cell- walls. 122 PRACTICAL BOTANY. REPRODUCTIVE ORGANS. DEVELOPMENT OF THE FLOWER. I. Examine young Capitula of the Sunflower with the naked eye : they occur in the same positions as the vegetative apical bud, but differ externally from these 1. In their greater bulk, and more especially in their diameter being larger than in these. 2. In their colour, which is usually darker. 3. In being covered externally by a large number of imbricated Bracts (or hypsophyllary leaves), which together form the general involucre. Select a very young capitulum, that is, one in which these characters can be recognised, but are not as yet very pronounced, and, having removed the largest external bracts, cut from it median longitudinal sections : treat with potash for about ten minutes, and mount in glycerine : observe with a low power 1. That in outline and general arrangement of parts the sections resemble those of the vegetative bud, but that the apical cone is broader, and more flat. 2. That the surface of the cone has an irregular outline, owing to the formation of a series of appendicular organs, which are developed in acropetal order, i.e. the smallest or youngest are nearest the apex, while on passing towards the periphery the size regularly increases. Put on a higher power, and study these organs in detail. DEVELOPMENT OF THE FLOWER. 123 Beginning at the centre : if the capitulum be young enough, there will be found, as in the vegetative bud, a naked apical cone, with a similar arrangement of tissues to that there observed. Passing from the centre, the external surface assumes an undulating appearance owing to the formation of 1. Bracteoles, leaf-structures, which arise similarly to the leaves as above observed, by outgrowth of the epidermis and subjacent tissue : as they grow older they curve towards the centre. [Note the formation of hairs of various types from single cells of the epidermis : this being a good opportunity for tracing their origin.] 2. The rudiments of Flowers, which appear in the axils of the bracteoles [i.e. on the side nearer the apex]. These are likewise produced from the epidermis and subjacent tissue, they are morphologically axillary branches. The development of the latter into the complete flower must be carefully studied, by comparison of those nearer the centre with older flowers nearer the periphery of the capitulum, or on capitula of various ages. It is obvious that flowers which have been cut in median section will be best fitted for this study. Note the following successive stages of development (a). Form of papilla, conical. (&). Apex becomes flattened. (c). Periphery of the flattened apex rises into a whorl of five small lobes ; these are the Petals, which are in the mature flower united in a gamopetalous Corolla. (d). Between the corolla, and the now depressed 124 PRACTICAL BOTANY. apex, rises a fresh series or whorl of five lobes, these are the young Stamens. About this stage may be seen externally, below the corolla, a slight protuberance on each side of the flower (as seen in section). This is the first appearance of the Calyx, which consists in the mature flower of two scaly sepals. N.B, This order of appearance of the floral whorls is not normal, but is the rule in the order Composite^. In the large majority of plants the calyx is developed first, then the corolla, and then the stamens. (e). Within the whorl of stamens there arise, at the margin of the now much depressed apex, the last series of floral organs, viz., two Carpels, which arch over the apical depression, and thus close in the cavity of the inferior ovary. (/). All the organs increase in size, while from the base of the cavity of the ovary, a papilla arises, which develops into a single anatropous Ovule, with one Integument, and small Nucellus. (For the development of the ovule cf. Helleborus, p. 130.) Cut horizontal (i.e. transverse) sections of a capitulum : treat as before : examine with a low power. Note the arrangement of bracteoles, with young flowers in their axils, round the central naked apex. The youngest flowers will appear simply circular in outline (simple papillae of stages a and 5) : older flowers will show successively (i). The five papillae of the Corolla (petals) uniting at an early stage into a gamopetalous corolla-tube. (Stage c.) THE STAMEN. 125 (ii). Five Stamens, alternating with the petals. (Staged.) (iii). Centrally two Carpels. (Stage e.) II. Take a mature flower of Helleborus fcetidus. Observe, and remove successively 1. The five Sepals, polysepalous, regular, inferior, and herbaceous. 2. Petals, number various, polypetalous, tubular, inferior. 3. Stamens, numerous, hypogynous, free. 4. Carpels, number various, apocarpous, superior. Examine a single Stamen, and observe that it con- sists of A a. thin stalk the Filament. A 1. two-lobed head the Anther. In a fully open flower note the lateral, longitudinal dehiscence of the anthers, and the dusty Pollen thus liberated. Examine a single Carpel; it consists of a lower thicker portion, terminated by a thin curved portion (the Style) ; on the inner surface at the top of the style is the Stigma. Slit a carpel open along the dorsal side, turn back the flaps, and observe the numerous ovules, attached, in two rows, to the ventral side of the carpel. STAMEN. III. All the following preparations should be made from materials hardened in alcohol, or better, fixed with saturated solution of picric acid, and then washed and hardened with alcohol. A. Cut transverse sections of a flower bud of Helle- 126 PRACTICAL BOTANY. lorus fcetidus, which was just ready to open, taking care that the anthers shall be cut through transversely. Neglecting the other parts, mount the sections of the anthers in glycerine, and examine with a low power. Note 1. The general outline of the section, and compare it with the form of the bi-lobed anther, as above observed. 2. The two large cavities one in each lobe. 3. The partial Septa, which originally divided each cavity into two Pollen-sacs or Microsporangia ; the anther has thus orginally four pollen-sacs, and these may sometimes be found still distinct even in almost mature anthers (cf. development of anther). A 4. single small Vascular bundle lying sym- metrically between the cavities, in the central part (or Connective) of the anther. 5. Pollen-grains or Microspores, mostly to be found lying free in the glycerine. Put on a high power, and observe that 1. The wall of the anther is composed of (a) An external Epidermis with a well-marked cuticle. Within this A (fr) ]ayer of cells with a fibrous thickening of the walls. (c) Immediately within (6) a narrow ill-defined band, consisting of the remnants of a transitory layer of cells, the Tapetum. A 2. point in the wall of each cavity, opposite the partial septum, where the cells are smaller, and the inner layer not spirally thickened ; this is the point of dehiscence of the anther. THE STAMEN. 127 3. Pollen-grains or Microspores are almost spherical, with smooth walls, and granular protoplasmic contents, in which may be made out, with difficulty, two nuclei. B. Mount in half glycerine half alcohol some almost mature pollen of Fritillaria imperialis, which has been previously preserved in alcohol, and examine with a high power. The grains have a smooth wall, and in the granular protoplasm may usually be seen two nuclei. N.B. If the grains be stained with hsematoxylin before mounting in glycerine and alcohol, the nuclei will be more easily made out. Mount and examine, as types of the various forms of the grains, the pollen of HeliantTius, Althcea, Cucurbita, CEnothera, Orchis (pollen-masses or pollinia), Mimosa, Cichorium, &c. C. In order to observe the germination of the pollen-grains, and formation of the pollen-tubes, use may be made of the moist chamber, described on p. 16. Mount some pollen-grains of HeliantJius in one hanging drop of a weak solution of cane-sugar in water (about 5 per cent.). Examine them with a high power, and note their form and the external configuration of their walls. Keep them at an ordinary temperature in the dark for a few hours : on again examining them, many will be found to have put out Pollen-tubes, filled with granular protoplasm, in which one or more nuclei might be detected. The same method may be used for the pollen of other plants, e.g. Orchids, species of Tulipa, Fritillaria, Nymphcea, &c. It 128 PRACTICAL BOTANY. will be found that the time of appearance of the pollen-tube will vary in different cases ; also that to obtain good results solutions of sugar of different strengths will have to be used. In most cases a solution of 10 per cent, or less will be found suitable. Development of Anther and Pollen. If transverse sections be made from very young buds, and successively from older ones up to the mature flower, the development of the anther and of the pollen may be traced. The material should be preserved in absolute alcohol (or strong methylated spirit), and the sections should be treated with half glycerine, half alcohol ; this should be left exposed to the air in a watch-glass, so that the alcohol may evaporate ; mount in pure glycerine. (Anhydrous staining reagents may be employed.) By following this method, sections may be prepared illustrating : 1. The formation of the four masses of tissue in the anther (two in each lobe), each of which subsequently becomes differentiated into : A (a) peripheral coat of cells of the tapetum, which take no direct part in the formation of the pollen, and A (6) central mass of pollen-mother-cells. 2. The division of each of the pollen-mother-cells into four special-mother-cells, by the gradual ingrowth of the wall of the mother-cell. 3. The separation of the members of the tetrads thus formed, and their subsequent development as pollen-grains. 4. The gradual disorganisation of the tapetum. 5. The development of the wall of the anther, as above described, and breaking down of the septum between the pairs of pollen-sacs. Compare similar preparations of the young anthers of Trades- cantia, and note the division of the pollen-mother-cells, without any gradual ingrowth cf the wall. Observe, as far as possible, the divisions of the nuclei of the pollen-mother-cells first into two, then into four ; also the two nuclei in the mature pollen-grain. CARPEL AND OVULES. 129 CARPEL AND OVULES. IV. The following preparations must be made from materials hardened in absolute alcohol (or methylated spirit) : Strip off the sepals, petals and stamens from an open bud of Helleborus fcetidus, and cut transverse sections of the Carpels. Treat the sections with one half pure glycerine, one half alcohol, and let the alcohol evaporate gradually. Mount in pure glycerine. Strasburger recommends that tlie transfer to pure glycerine should be made before the sections are cut. Examine first with a low power, and observe 1. The Carpel, having a structure not unlike that of an ordinary leaf. Note the suture or junction of the two margins of the carpel which thus incloses a central cavity. 2. The Ovules (Macrosporangia) seated in this cavity, and attached near the margins of the carpel (it has already been noted that there are two rows of ovules in each carpel, therefore at most only two ovules appear in each section). The form of the ovule is anatropous ; it consists of the following parts : (a) The Funiculus, or stalk, which adheres through the greater part of its course (as the Raphe) to the A body of the inverted ovule. procambium bundle, connected with a bundle at the margin of the carpel, traverses it longitudinally. The body of the inverted ovule consists of K 130 PRACTICAL BOTANY. (b) One Integument several layers of cells thick, united with the funiculus, and covering the body of the ovule completely, excepting a narrow channel (Micropyle) near the apex of the ovule. Within this lies (c) The Nucellus, a mass of cellular tissue in which is embedded (d) The Embryo-sac (Macrospore), a large oval cell, situated a short distance below the apex of the nucellus. Examine the embryo-sac with a high power, and observe 1. The granular, vacuolated protoplasm which fills it embedded in this are to be found ; A 2. large central nucleus. 3. At the micropylar end of the embryo-sac, three cells, with clearly denned nuclei. Two of these (the Synergidae) fill the apex of the sac, the third (the Oosphere) being placed laterally, a little below the apex. 4. At the posterior end of the sac are three cells (the Antipodal cells), also with clearly defined nuclei. Note the Tapetum, consisting of cells more or less disorganised, which partially or completely surround the embryo-sac. If similar sections be cut from buds of Helleborus fmtidus of various ages, and be treated in the same way, the development of the ovule, and more especially of the embryo-sac, may be followed, and the various stages of it may be observed. Make similar sections of the ovary of species of Lilium, or Yucca, and compare them with the above. With the exception of a second integument being present in these cases, the structure of the ovule will appear to correspond to that of ffelleboms. FERTILISATION. 131 FERTILISATION. I. Cut median vertical sections through the stigma and upper part of the style of a flower of Datura Stramonium which has just faded. Mount in dilute glycerine, and examine first with a low power. Note 1. The closely-packed tissue covering the Stigmatic surface, the superficial cells of which are slightly elongated perpendicularly to the surface as hairs. 2. The more lax Cortical tissue of the style, with numerous intercellular spaces, which appear dark under the microscope. A 3. central band of more transparent tissue without intercellular spaces (Conducting tissue). 4. Small vascular bundles, two in number, running up the style ; these may or may not be present in the section, according as it has been cut. 5. Pollen-grains adhering to the surface of the stigma; from them pollen-tubes, similar to those grown in sugar solutions (cf. p. 127) may often be traced penetrating the tissue of the stigma. Now gently boil the sections in the dilute glycerine over a spirit lamp, and examine again. Observe 1. The Pollen-grains as before. 2. Pollen-tubes, which may be traced from them through the now more transparent tissues of the style ; they may be recognised by their densely granular contents. Other flowers besides the above may be used e.g. species of (Enothera, &c., or any flower in which the style and stigma are of considerable size. K2 132 PRACTICAL BOTANY. II. Pick out gently a number of ovules from an ovary of a flower of Datura Stramonium, which has just faded, and mount in dilute glycerine. Observe 1. The Campylotropous Ovules, with curved body. 2. Pollen-tubes, which are often to be found with the end applied closely to the micropyle. Strasburger observed the process of fertilisation itself directly in Torenia asiatica, Gloxinia, and also in Orchids, Monotropa, and Pyrola. His method was to open the ovary of a flower a short time after pollination, and detach and mount the ovules in a 3 per cent, solution of sugar. DEVELOPMENT OF THE EMBRYO. i. Dicotyledon. Pick out the ovules from an ovary of Capsella Bursapastoris, which has attained about half the ultimate size of the mature fruit. Treat with dilute potash, and examine with a low power. Observe 1. The form of the ovule (campylotropous, i.e. with a curvature of the body of the ovule). 2. The Funiculus, or stalk. 3. The Integuments. 4. The Micropyle, not very easily seen : a pollentube may often be observed entering the micropyle. A 5. large central cavity (the Embryo-sac), which is curved like the whole ovule. In this may be seen, more or less distinctly 6. The Embryo. CAPSELLA. EMBRYO. Io3 To study the structure of the embryo, either longitudinal sections of the ovule must be cut, and the embryo be thus laid bare, or the embryo must be removed from the ovule. The former is the more accurate method, though the latter is much the easier : we will therefore adopt the latter. Press gently with a needle upon the cover slip of the above preparation, so as to burst the ovules : the embryo will escape in some cases without injury ; neutralise the potash with dilute acetic acid. The structure of the embryos, which now lie freely suspended in the fluid, may be easily studied. Apply the same method for the preparation of embryos, from ovaries of various ages, both younger A and older than that first taken. series of prepar- ations may thus be obtained illustrating various stages of' development of the embryo, such as are figured in ordinary Text-books. Note more especially the following successive stages of development : 1. The Suspensor, consisting of one or more cells, and terminated by a single Embryonic cell. 2. The embryonic cell divided into octants arranged in two tiers, the terminal cell of the suspensor (Hypophysis) encroaching between the four lower octants. 3. The octants so divided up as to form three layers of cells, which have been distinguished as (a) the external Dermatogen ; (b) the Periblem ; (c) the central Plerome. 4. The two Cotyledons formed by lateral outgrowth from the upper tier of octants, the apex of the Radicle 134 PRACTICAL BOTANY. derived from the hypophysis, the hypocotyledonary stem from the lower tier of octants. 5. Other parts as before. The Apical cone or Plumule formed between the cotyledons. ii. Monocotyledon. Treat ovules of Alisma Plantago in the same way, and observe the following stages of development : 1. Suspensor and Embryo consist of a single short series of cells, produced by transverse divisions. 2. The terminal cell divides longitudinally into four (first tier). 3. The second, third, and fourth cells from the end also divide successively (second, third, and fourth tier). 4. The cells of the body of the embryo divided (as in Capsella) so as to form three layers (a) external Dermatogen, (&) Periblem, (c) central Plerome. A 5. lateral depression of the surface, at the level of the second tier. At the basal lip of this the Apical cone of the plumule is formed. The single Cotyledon is formed from the first tier. The Radicle from the third tier. The Apex of the root from the fourth tier. Compare these results with those obtained in Capsella. For obtaining preparations of the embryo in situ, and of the Endosperm surrounding it, the ovary of species of Potamogeton will be found to be good material : it should be previously hardened in spirit. Cut longitudinal sections of a single carpel, parallel to the flattened sides : they