Sporangia Structure and Spore Examination

filled with small tetrahedral spores. N.B. In preparing the sections the spores are often washed out from the sporangia. LYCOPODIUM. SPOROPHORE. 185 Examine a good section of a sporangium under a high power; the wall will then be seen to be of approxi- mately uniform thickness throughout, and consists of A a. well-marked outer layer of cells of considerable size. An b. inner ill-defined band, consisting of the remains of disorganised cells. If the wall be observed in surface view the cells will be seen to be of sinuous outline, and somewhat elongated, with the exception of a zone which indicates the line of ultimate dehiscence of the sporangium : here the cells are shorter, and the walls are straight. The line of dehiscence may also be recognised in the wall as seen in section. Note also the structure of the Spores ; they have the form of a rounded tetrahedron, and the outer wall is covered with peg-like projections. By cutting similar median longitudinal sections of cones in various stages of development, and comparing them, the history of development of the sporangium may be traced. It may be seen that the sporangium arises as a multicellular outgrowth of the upper surface of the leaf ; at an early stage the archesporium may be recognised as a hypodermal cell, or possibly several cells : the superficial layer of cells above it gives rise by division to three layers ; of these the innermost is the tapetum, which, together with the next outer layer, is disorganised as develop- ment proceeds, while the outermost layer is still persistent in the mature sporangium. The archesporium meanwhile divides to form numerous spore-mother-cells, each of which divides tetrahedrally, and gives rise to four spores. The proper conditions for germination of the spores of our native species not having as yet been discovered, reference should be made to the Text-books for further information as to the life-history of Lycopodium. B. FILICINEJE. ASPIDIUM FILIX-MAS (The Male Shield Fern). A. MATURE SPOROPHORE. I. External Characters. I. Taking a well-grown plant of the common Male Fern in summer, wash the soil away from the roots, and observe the following external characters : A. The Stem is oblique and ascending. It is not branched at its apex ; its surface is covered by the persistent bases of the Leaves, which are densely covered by numerous brown scaly hairs (Ramenta). B. The Leaves, the most prominent of which are i. The fully-developed green leaves of the current year ; these are large and of complicated structure, and the following parts may be recognised : A a. long almost cylindrical leaf-stalk which is traversed by two longitudinal, lateral ridges or reduced wings. This leaf-stalk supports 1}. The numerous Pinnae, which are arranged in two lateral rows, corresponding in position to the lateral ridges above mentioned. Note that the arrangement of the nerves in the segments of the pinnae is based upon repeated bifurcation of the stronger nerves. On the under side of the pinnae will frequently be found MALE FERN. SPOROPHORE. 187 c. Sori, which are roundish groups of small stalked bodies (Sporangia), covered by a kidney-shaped Indusium. ii. The bases of the leaves of previous years will be seen, covering the lower part of the stock or stem externally. Observe that lateral buds are frequently to be found connected with these, being attached to their posterior side, near to their point of junction with the stem. iii. Nearer the apex of the stem than the expanded leaves of the current year, and completely covering it, are young leaves, densely covered with brown scales (Ramenta) ; these, together with the axis, constitute the Apical bud. Note that the apex of each such leaf is rolled up like a crozier (circinate vernation). N.B. Here, as in most Ferns the development of the leaves is very slow ; the young leaves seated round the apex represent the foliage leaves of the two succeeding years. C. The Roots are rather thin and brown, with transparent apices : they are inserted on the bases of the leaves, close to their junction with the stem : the branching of the roots is monopodial, and the branches appear in acropetal succession. The stem of Aspidium Filix-Mas does not branch at its apex : the same is as a rule the case in the erect stems of Ferns (e.g., Tree Ferns) where the leaves are closely crowded. In those Ferns in which the axis is elongated, a terminal branching is more frequent : thus in Pteris aquilina there is a dichotomous branching. In other forms the new axes appear in connection with the leaves, either at the base of the leaf (Aspidium Filix-Mas), or in various positions on the flattened upper part of the leaf (many species of Atpleniurri). 188 PRACTICAL BOTANY. IT. Anatomical Characters to be observed with the naked eye. II. Having observed the above external characters, remove the roots, keeping the transparent apices of the young roots, as well as the thickest parts of the old roots : these should be preserved in alcohol for further treatment. Starting from the posterior end of the stock, cut off successively the persistent bases of the old leaves about J inch above their insertion on the stem. Observe the lateral bud borne by some of the leaves on the posterior side of the leaf-stalk near its base : observe also that the roots spring from the bases of the leaves, close to their insertion on the stem. Cut off about 2 inches of the posterior end of the stem exposed as above, and boil it in dilute hydrochloric acid till the parenchyma 'is soft: for further treatment of this see below. Meanwhile smooth the cut end of the remainder of the stock with a razor, so that it may present an even surface of transverse section, and observe a. The great irregularity of outline, due to the close crowding of the bases of the leaves. 5. The dark brown band of Sclerenchyma border- ing the periphery of the section. c. The great bulk of the stem consisting of yellowish Parenchyma, with very bulky central Pith. d. Round the latter a number of isolated, large Vascular bundles, forming an interrupted ring. .. Outside these, and running out into the leaves, MALE FERN. SPOROPHORE. 189 are numerous smaller bundles of the leaf-trace, which appear to be less regularly arranged. III. Divide the stock, including the apical bud, into two symmetrical halves by cutting it in a median longitudinal plane : smooth one of the cut surfaces with a razor, and observe a. That the stem is of almost equal thickness throughout its length, i.e., it is roughly cylindrical. &. That its external conformation is very irregular by reason of the closely crowded insertion of the leaves. c. The bulky central Pith as before. d. The large vascular bundles (d above), which are not continuous in direct longitudinal lines, but form an interrupted series. e. The smaller bundles of the leaf-trace (e above), which in some cases may be followed, after a little careful dissection of the parenchyma which surrounds them, from one of the larger bundles of the central system into the base of one of the leaves. Slice away carefully the external tissues of the posterior part of the stock, so as to lay bare the central system of larger bundles : it will then be seen that these form a continuous network with large meshes, and that each mesh is opposite the point of insertion of one of the leaves, hence it is called a foliar gap. Observe also that the vascular bundles of the leaf are given off from the margin of its own mesh. IV. Confirm these observations by the dissection of the part of the stock macerated in dilute hydrochloric acid. The parenchyma, being thus rendered soft and friable, may be easily removed, leaving the vascular system as a net-work of stronger bundles, which gives 390 PEACTICAL BOTANY. off numerous weaker bundles from the margins of its meshes : these weaker bundles run out into the leaves. V. Remove from the apical bud the large quantities of scaly hairs (ramenta), so as to lay bare 1. The young leaves, with their circinate vernation. 2. The broad apex of the stem with leaves in various stages of development around it. 3. The young roots, which will be found already present on the bases of very young leaves. 4. The young buds, which may be observed at a very early stage on the posterior side of the leaves. Though the above is the general type of bundle-arrangement for Ferns with ascending or upright stems, in Ferns with creeping stems other modes of arrangement are found, which, however, may be regarded as being related to the type above described. Thus (1) in the Hymenophyllacece, &c., there is a single central bundle, an arrangement which is found also in the young seed- lings of other more complex forms ; (2) in species of Davallia and others with horizontal stems, the ring consists of two stronger bundles, one running parallel to the upper, the other to the lower surface; between these are on each side several smaller bundles, which, together with the two stronger ones, form an interrupted ring as seen in transverse section ; (3) in other cases there are several (in Pteris two) concentric rings of bundles, which give off branches to the leaves, &c. III. Microscopic investigation. VI. Cut transverse sections of the stock : it is hardly to be expected that a transverse section of so bulky a stem as this could be cut so uniformly thin that the structure of all the tissues could be well seen; it is better therefore to cut a number of sections, each extending over a comparatively small area, and to study the various tissues separately. Mount some in (1) MALE FERN. SPOROPHORE. 191 glycerine or glycerine jelly, others (2) in acid aniline sulphate, others (3) in Schulze's solution. Examine under a low power, and observe successively the fol- lowing tissues, starting from the periphery of the stem : a. An Epidermis, consisting of a single, somewhat irregular and ill-defined layer of cells, with dark brown outer walls : their arrangement is disturbed at the point of insertion of the scaly hairs, which appear as plates of cells, one layer in thickness, rising obliquely from the epidermis. Beneath this is 1. The Ground tissue, which is differentiated as i. An outer narrow band of tissue, with rather thick, colourless, pitted walls, and cell-contents with much starch : there are no intercellular spaces. A ii. band of Sclerenchyma with thick, yellow, lignified, obviously stratified, and pitted walls, cell- contents as in (i), and no intercellular spaces. This merges gradually into iii. The bulky central mass of ground-tissue, in which the vascular bundles are embedded. It con- sists of cells with comparatively thin, pitted, cellulose walls, protoplasmic contents with much starch, and with intercellular spaces. On the external surface of those parts of the cell-walls which adjoin the intercellular spaces numerous small projecting spikes may be observed : it may be readily seen that these originate in connection with the formation of the intercellular spaces. Internal glandular hairs are also found in the intercellular spaces ; they are attached by narrow stalks to single cells of the parenchyma : the globular head contains when fresh a resinous secretion, which is soluble, but not readily, in alcohol. c. The Vascular bundles, of elliptical outline ; 192 PRACTICAL BOTANY. they are embedded in the ground-tissue, and are sharply circumscribed by a narrow, light brown layer of cells without intercellular spaces : this is the Bundle- sheath. Among the tissues inclosed by this sheath, note that a large central mass may be distinguished as consisting for the most part of elements with large cavity, no cell-contents, and rather thick walls with a peculiar marking : this is the Xylem * Between this and the bundle- sheath is a broad band of tissue with thin, bright-looking walls, and with protoplasmic contents : this is the Phloem. Since the xylem is surrounded by the phloem, this bundle is said to be of the concentric type. In the sections treated with Schulze's solution, note that the walls of the inner ground-tissue stain blue, and that starch is found in the cells : that the bundle- sheath appears browner than before, that the walls of the phloem stain blue (cellulose), and the contents yellowish : that the walls of the chief constituents of the xylem stain yellow (lignified). In the sections treated with acid aniline sulphate observe the yellow coloration of the walls in the xylem, while those of the phloem are not stained. VII. As the vascular bundles of the leaf-stalk are better fitted for minute observation, and are better types of the concentric bundle of the Fern than those of the stem, cut thin transverse sections of the lower part of the petiole. Having previously noted with a low power that in their main features the tissues resemble those above observed in the stem, examine the structure of one vascular bundle under a high power, and starting from the periphery of it note successively MALE FERN. SPOROPHORE. 193 1. The Bundle-sheath, a single layer of cells with yellowish walls, and yellow granular contents. N.B. There are no intercellular spaces in this layer, nor in any of the tissues surrounded by it. Treat a thin section with sulphuric acid, and note that the walls of the bundle-sheath retain a sharp contour, while those o the rest of the tissues swell, and become more or less disorganised. 2. The Phloem-sheath, which is a band of tissue of varying thickness at different parts of the bundle, being thin at the poles of the elliptical bundle, and thicker at the sides : it consists of cells of roundish form with cellulose walls, and protoplasmic contents, with starch. Note that each of the outermost cells of the phloem-sheath is as a rule opposite one cell of the bundle -sheath : this points to a common origin of the two layers. In the bundles of many Ferns, e.g., in the "Rhizome of Pteris, the phloem-sheath appears as a single layer of cells. 3. At the inner limit of the phloem-sheath are found elements with thick cellulose walls and narrow cavity : these constitute the Protophloem of Eussow. 4. Internally lies the broad band of true Phloem, which is composed of two tissue-forms a. Sieve-tubes, which appear in the transverse section as polygonal, with their thin, cellulose walls, which are lined by a delicate protoplasmic membrane including numerous highly refractive granules. &. Parenchymatous cells with thin walls and pro- toplasmic contents. o 194 PRACTICAL BOTANY. 5. Centrally lies the Xylem, in which also two constituents may be recognised a. Tracheides, which appear polygonal in transverse section, and have large cavities, with no cell-contents : the walls are thick and lignified, and show a peculiar structure which will be explained by a comparison with what is seen in longitudinal sections. 6. Parenchymatous cells, with cellulose walls, and protoplasmic contents and starch. These cells are distributed evenly throughout the xylem, and also form a band surrounding it completely. N.B. The parenchyma in both phloem and xylem being fundamentally of similar nature may be united under the general term Conjunctive parenchyma. Cut similar transverse sections of the stem of Pteris or Davallia, and note that the outlines and arrangement of the tissues are more regular than is the case in Aspidium. VIII. Cut longitudinal sections of the stem of the Male Fern. First take radial sections of the peripheral tissues, and treat as above : note 1. The Epidermis, with scaly hairs. 2. The sub-jacent ground tissue, and especially the Sclerenchyma, consisting of cells of short, prosenchymatous form, with brown pitted walls, and cell- contents : note the gradual transition from the scleren- chyma to 3. The colourless ground-tissue, with short paren- chymatous cells, and large intercellular spaces. IX. Then cut longitudinal sections, so as to pass tangentially through the central network of bundles : treat some sections with Schulze's solution, and mount MALE FERN. SPOROPHORE. 195 others in glycerine. Note the several tissues above observed in the transverse sections : they have in this section a corresponding position relatively to one another : by reason of the frequent splittings and fusions of this bundle-system the several elements will appear contorted and twisted, but this does not materially affect their general arrangement. Examine under a high power, and observe A. In the Xylem of the bundle a. The Scalariform tracheides, which are the main constituents of the xylem : they are elongated prosenchymatous elements, with ladder-like marking of the lateral walls; this is due to the presence of regularly arranged, transversely elongated, bordered pits. Take especial notice of the appearance of the lateral walls as seen in longitudinal section where two tracheides are contiguous with one another ; and compare them with parts of the wall which adjoin. I. Cells of the Conjunctive parenchyma interspersed among the tracheides. c. Tracheides with spiral marking ; these are the first-formed xylem elements, or Protoxylem. B. In the Phloem observe a. The Sieve-tubes, which are also elongated elements with pointed ends : the surfaces of the walls which separate contiguous sieve-tubes are covered with numerous sieve-plates (best seen in sections treated with Schulze's solution), to which round, highly refractive granules adhere : these stain yellow with Schulze's solution. Note especially the irregular outline of the walls when seen in longitudinal section. o2 196 PRACTICAL BOTANY. N.B. The sieve-tubes are better seen in similar sections of the Rhizome of Pteris. b. Cells of the conjunctive parenchyma inter- spersed among the sieve-tubes. X. Separate some pieces of the vascular bundles from the surrounding tissue, and warm them gently in a test tube with potassium chlorate and nitric acid, till the elements of the bundle may be separated easily one from another ; then stop the action by diluting with water, and mount in water. By preparing them in this way the tracheides, (fee., may be subjected to separate examination, and their form and structure may be made out. Apply the same process to the sclerenchyma, and observe the form and marking of the walls of its constituent elements. XI. From around the apical bud of a well-grown plant of the Male Fern remove successively the bases of the leaves of previous years, those of the current year, and finally the larger circinate leaves, which would have unfolded in the following year. Carefully remove the smaller ones with a scalpel, and then with forceps gradually pull off the large mass of brown scales, which completely cover the extreme apex. With a camel'shair brush remove the bases of these scales, together with the youngest of them, which will still remain round the punctum vegetationis; after this treatment it will be easy to observe with a pocket lens 1. The Apical cone (punctum vegetationis), a rounded papilla, occupying a central and terminal position in the flattened apical region. 2. The young leaves, situated round the apical cone, and successively larger the further they are from MALE FEKN. SPOKOPHORE. 197 the apex. Note the circinate curvature which appears at an early period in their development. XII. With a sharp razor, wet with water or with very weak spirit, remove the extreme apex of the punctwm, vegetalionis, taking care to cut accurately in a trans- verse plane : mount first in water, and examine with a low power. If the section be thin enough, it will be seen that a cell of triangular outline occupies the centre of the apical cone, while the cells immediately surrounding it are arranged in more regular order than those at a greater distance. This cell is the Apical cell, and the cells surrounding it have been derived by cell-division from it, and are called therefore the Segmental cells : it may readily be seen that these again undergo subdivision. N.B. If the section be not sufficiently transparent, it may be treated with very dilute potash and weak glycerine, which will clarify the tissues, and make the cell-walls more distinct. XIII. From the apex of another plant cut median longitudinal sections ; mount first in weak glycerine, and a little very dilute potash may be added if the sections are not transparent enough. If any one of the sections has passed through the apical cone, in a median plane, the Apical cell will be seen presenting a wedge-like appearance, and the cells around it will show, in the regularity of their arrangement, that they have been derived from segments successively cut off from the apical cell. It may be concluded from the observation of transverse and median longitudinal sections that the form of the apical cell is that of a three-sided pyramid. 198 PRACTICAL BOTANY. The structure and mode of origin of the youngleaves should also be observed in the median longi- tudinal sections. The Eoot. XIV. Cut transverse sections of the root of the Male Fern, selecting for that purpose the thickest part of an old root : mount in glycerine, and observe 1. There is not any well-marked epidermis : single superficial cells have grown out as root-hairs, remnants of which may still be seen. 2. The greater part of the section consists of the bulky, brown-walled Cortex, of which the outer parts are thin-walled ; but, passing inwards, there is a sudden increase in thickness of the walls, so as to form a dense sclerenchymatous ring : this surrounds 3. The Bundle-sheath, which consists of a single layer of cells flattened tangentially, and having the usual dotted marking of the radial walls. [N.B. This may be difficult to observe as the radial walls are often pressed out of shape.] Within this layer lies 4. The Phloem-sheath, which usually consists of two layers of cells, with thin walls, and obvious protoplasmic contents. The vascular tissues inclosed within these layers are arranged according to the ordinary radial type ; thus there will be seen 5. Two groups of Xylem abutting on the phloem- sheath, and composed of Tracheides of various size, the largest being near the centre of the root: the two originally separate groups of xylem unite at the centre by formation of fresh tracheides, and together MALE FERN. SPOROPHORE. 199 form a flat band which traverses the root longitudinally. Alternating with the groups of primary xylem at the periphery of the vascular cylinder are 6. Two groups of Phloem, consisting mainly of Sieve-tubes having the same characters as those of the stem. Scattered among the vascular elements are cells of conjunctive parenchyma. Note that one or two cells of tlie bundle-sheath opposite the groups of xylem are larger than the rest : these are the rhizogenic cells, which might have been the starting points of lateral roots : the latter are formed at an early stage of development of the tissues of the root, i.e., near to the apex ; if transverse sections be made through the young part of a root, lateral roots may be found in course of development in positions corres- ponding to the rhizogenic cells. If transverse sections of the root be cut at a point not far removed from the apex, it will be seen that the xylem is not yet developed at the central part of the vascular cylinder, while the peripheral parts may be fully formed : thus the development of the xylem is centripetal, the root is diarch, and the arrangement of the vascular tissues is radial. XV. Cut median longitudinal sections of the apex of a root, which has been hardened in alcohol (of course at most only one absolutely median section can be obtained from a single root : it will be found convenient to embed the apex of the root in cocoa-butter, or to hold it between pieces of pith or carrot). Mount in glycerine, and examine first with a low power, and choose out those sections in which there is a symmetrical arrangement of tissues around a single, large, apparently three-cornered Apical cell, which lies at some distance from the extreme apex. Note 1. That the orientation of the apical cell is con- 200 PKACTICAL BOTANY. stant, i.e., one corner is directed towards the older part of the root, while the side opposite that corner, i.e., the anterior face or base of the cell, is at right-angles to the axis of the root. 2. That around the apical cell are regularly arranged Segmental cells, which have successively been cut off from it by walls parallel to the sides of the apical cellOf these a. Those successively cut off from the base form the Root-cap, dividing up by regularly arranged walls into a mass of regular cells. 5. Those cut off from the sides of the apical cell form the body of the root : these also divide by walls in regular succession. Observe carefully the arrangement of these walls, and by comparison of several sections ascertain their order of succession, and their relation to the various tissues of the root above described. XVI. Cut successive transverse sections of the apex of a root which has been hardened in alcohol. (This may easily be done if the root be held between pieces of pith, or by embedding in cocoa-butter.) If possible keep all the sections in their proper order of succession, and mount in glycerine. Examine with a low power, and choose out those in which the large apical cell is to be seen. Observe carefully 1. The form of the apical cell, apparently three- sided : combining this result with that obtained by examination of the longitudinal sections ; the form of the whole cell must be a three-sided pyramid. 2. The Segments are arranged in regular order round it, and are cut off successively from the three sides. MALE FERN. SPOROPHORE. 201 3. Note the mode in which the several segments are further divided up. Next examine a section which has passed through the root-cap immediately above the apical cell : this will include the young segments cut off from the base of the apical cell by transverse walls, and destined to form the root-cap. Note the first divisions of these segments by walls arranged crosswise : it may be seen that these walls do not coincide in position in successive segments. The Leaf. XVII. Cut transverse sections of a pinna of a leaf of the Male Fern which has no sori upon it : mount in weak glycerine, and observe with a low power that the outline of the section shows the leaf to be of equal thickness throughout, except where traversed by vascular bundles : at those points the pinna is thickened, the lower surface projecting convexly. Examine with a high power, and observe successively the following tissues, starting from the upper surface : A 1. regular Epidermis with a thin cuticle : the epi- dermal cells contain chlorophyll : there are no stomata. 2. The Mesophyll consists in its upper part of thin-walled cells containing chlorophyll, and with small intercellular spaces; this passes by gradual transition into the lower part, where the intercellular spaces are larger, and the form of the cells less regular. 3. The lower Epidermis, the cells of which also contain chlorophyll : numerous Stomata are present : 202 PRACTICAL BOTANY. note the form of the two Guard-cells as seen in transverse section, and their position in relation to the epidermis. 4. Here and there Vascular bundles, of circular appearance in transverse section, will be found embedded in the mesophyll : the larger of these correspond in position to the swollen ribs of the pinna. Note the Bundle-sheath as a continuous layer of cells, which completely surrounds the circular bundle, and within this the xylem and phloem elements similar to those of the stem : the bundles show a tendency to the collateral type, the xylem being nearest to the upper surface of the leaf. XVIII. Cut tangential sections (or strip off the epidermis) from (a) the upper, and (ft) the lower surface of the leaf : mount as before, and compare them. (a.) The epidermis of the upper surface will be found to consist of cells with sinuous outline, and protoplasmic contents, with chlorophyll : no stomata will be found. (5.) The epidermis of the lower surface consists of cells similar to the above; there are stomata with two guard-cells. The development of these stomata may be studied with advantage in young leaves, by stripping off the epidermis, or by cutting tangential sections. Special attention may be given to the peculiar case of Aneimia. The, Sporangia. XIX. Cut transverse sections through pinnae of leaves which bear Sori, taking care that the sections shall MALE FERN. SPORANGIA. 203 pass through one or more sori. Mount as before, and examine with a low power. Note 1. The structure of the pinna, as above described. 2. Opposite to, and seated upon a rib will be found the membranous Indusium, which, like an umbrella, covers over , 3. The Sporangia, which are biconvex-lens-shaped, brown, stalked capsules, attached to the rib, and filled with 4. Numerous roundish, brown, unicellular Spores. Observe more closely the structure of the single sporangium. It is composed of i. The Stalk, which is of considerable length, and usually consists of three rows of cells. Stalked glandular bodies are often found as lateral branches on the stalk of the sporangium in this species. ii. The Capsule, which has the form of a biconvex lens, and consists of a marginal series of cells with thickened walls, which constitute the 1 ring , and thinner- walled, flattened cells, which together form the lateral walls of the completely closed sporangium. Note sporangia in which the lateral walls have been ruptured transversely, the ring having straightened itself out with sufficient force to tear the more delicate lateral walls : by this means the spores are liberated. Examine single spores under a high power ; they are unicellular bodies, having a brown wall, with external band-like outgrowths of the exospore or outer layer of the wall. All the spores are alike (Homosporous). The various stages of development of the sporangium may be found in any sorus in which only the first sporangia have come 204 PRACTICAL BOTANY. to maturity. Note especially in such sori tlie following stages of development : A i. simple, hair-like process, consisting of a single cell, or of two separated by a transverse wall. ii. The upper cell divided up so as to consist of a central tetrahedral cell (archespore), surrounded by a single layer of cells, which form the wall. iii. The central cell or archespore is divided into . One cell, or a group of cells, lying centrally, which gives rise to the mother-cells of the spores, and finally to the spores themselves. A b. layer of transitory tapetal cells, which surround a, and are ultimately absorbed. B.THE OOPHORE. I. Dry some of the leaves of the Male Fern, which bear sori, on a piece of paper : the spores will then be set free by the rupture of the sporangia, and they may thus be collected in large quantities. Sow some of them on damp earth : keep them moist, and sheltered from direct sunlight : they will then germinate, and after a few weeks the surface of the soil will be found to be covered with small, green, flattened bodies, each of which is an individual Prothallus. If it be desired to follow the germination of the spore, and the first stages of the development of the prothallus in detail, the spores may be placed in a hanging drop in a moist chamber, as described, p. 16. But for all ordinary purposes it will suffice to pick off young prothalli, from time to time, with a needle from the surface of the soil on which spores have previously been sown : by this means a series of preparations illustrating the various stages of development of the prothallus may be obtained. Note in such a series of preparations, under a low power 1. The bursting of the outer coat of the spore, and the protru- sion of the inner coat through the slit. MALE FERN. OOPHORE OR PROTHALLUS. 205 2. The formation of An a. aerial portion, containing chlorophyll, and undergoing repeated cell-divisions, which result in the development of a flattened, roughly triangular, expansion. A b. root-hair, which remains undivided, does not contain chlorophyll, and grows downwards into the soil. 3. In older prothalli of the series note an incurving of the margin of the part more remote from the original spore, this is due to the slower growth of that part and the more rapid growth of the lateral parts ; at the base of this depression is one wedge- shaped apical cell, from which segments are cut off alternately on opposite sides. N.B. The identity of the apical cell and regularity of the segments are lost in the later stages of development. II. Examine a single prothallus with the naked eye, and observe 1. The form, which is flattened, and more or less kidney-shaped, with a depression of the margin, at the base of which is the Organic apex of the prothallus. Note that the central part of the prothallus is often perceptibly thicker than the periphery : this thicker part is called the Cushion. 2. The position of the prothallus while growing ; it is usually oblique to the surface of the -soil. 3. The Root-Hairs, which spring from the under surface of the cushion, and run downwards into the soil. 4. The green colour, due to the presence of chlorophyll: the prothallus is thus capable, under suitable circumstances, of carrying on the process of elaboration of fresh organic substances. III. Wash a fresh, well-developed prothallus carefully in water, so as to remove the soil from the root-hairs : 206 PRACTICAL BOTANY. mount it whole, in water, with the lower surface directed upwards, and examine it with a low power. Observe again the chief points above noted with the naked eye which are now more plainly seen, and note especially 1. The form and structure of the cells in the lateral, thinner portions of the prothallus ; they are polygonal, and have thin cellulose walls, and protoplasm containing a nucleus, and numerous chlorophyll grains : the cells at the margin are often extended as hair-like outgrowths. 2. The cells composing the cushion are of similar structure, but are aggregated in a mass more than one layer of cells in thickness : many of the cells will be seen to have grown out as root hairs. 3. The depressed Apex of the prothallus, which is occupied, not by a single wedge-shaped cell, as is the case in early stages of development [see above, small type, p. 205], but by a closely aggregated series of marginal cells, with thin cell-walls, and every appearance of recent and repeated cell-divisions. 4. The Antheridia, which are hemispherical outgrowths, situated chiefly on the posterior and lateral portions of the under side of the prothallus. 5. The Archegonia, which are situated on the cushion near to the organic apex of the prothallus ; the multicellular Neck of the archegonium projects from the surface of the prothallus as an elongated cylindrical structure. Under the low power select one mature antheridium, and, without moving the slide, adjust the higher power so as to observe the structure of the same antheridium in detail. It will then be seen that it consists of MALE FERN. OOPHORE OR PROTHALLUS. 207 A a. wall, composed of a single layer of narrow cells ; this completely surrounds I. The mother-cells of the Antherozoids, which are small, and not very numerous. Other antheridia may be found which have already burst the outer wall; in these the contents of the mother-cells may perhaps be seen escaping from the ruptured antheridium as spiral Antherozoids, endowed with active movements. If a preparation showing motile antherozoids be treated with a weak solution of iodine, the movements will cease with, the death of the antherozoids, which will assume a brown staining, while the cilia attached to the anterior ends of. them will then be clearly seen. Select under the low power one mature Archego- niurn, and then observe it in detail under the higher power. If the neck be vertical, which would under the circumstances be the natural position, there will then be seen, on focussing down upon it, four cells composing the wall of the neck, and surrounding one cell, the Canal cell. IV. Treat some prothalli with a saturated solution of picric acid in water for some hours. Wash them with water, and then harden them gradually by successive treatment with alcohol of 50 per cent., 70 per cent., and finally with absolute alcohol or strong methylated spirit. [N.B. The preparations described below may also be made from fresh material, but the results will not be nearly so good as if the above method of fixing and hardening be adopted.] Hold a prothallus thus prepared between pieces of pith, or imbed as directed on p. 4 &c. ; then cut 20S PRACTICAL BOTANY. sections perpendicularly to the surface of the pro- thallus, and so as to pass through the cushion, following the organic axis from base to apex. Mount in one part glycerine and one part water, and examine first with a low power. The lower surface may easily be recognised by the presence of root-hairs, and on this lower side, chiefly near to the apical end of the section which is characterised by its small cells with thin walls, will be found Archegonia ; these may be recognised by the multicellular neck, which projects beyond the surface of the section. [N.B. In some cases the canal of the neck may appear of a deep brown colour : these are old archegonia which have not been fertilised, and they must be disregarded.] Select one archegonium of full size and healthy appearance, and examine it under a high power. Observe that it consists of A A. Central series of three cells, which may be distinguished as a. The Canal-cell : this is oblong in form, and its walls are subject to mucilaginous degeneration; it occupies the channel of the neck, and has been above alluded to as being visible when the neck of the archegonium is seen from above. I. The small Ventral Canal-cell, which lies imme- diately below the oblong canal- cell, and is of rounded form. c. The Oosphere, which is of relatively large size, and roughly spherical form ; it is embedded in the tissue of the cushion, and consists of a dense mass of granular protoplasm. MALE FEKN. OOPHORE OR PROTHALLUS. 200 A B. Neck, which is composed of cells arranged in four rows, constituting together a cylinder or tube, one layer of cells in thickness : this projects from the surface of the prothallus, and incloses the cells (a) and (5) of the central series, while (c) the oosphere is embedded in, and surrounded by, cells of the cushion. At the end of the section more remote from the apex may be found Antheridia. Select one fully developed, and it will be seen to consist essentially of an outer wall, one layer of cells in thickness, which incloses a central mass of cells, the contents of which may be seen to be rounded off, and to have assumed the form of a closely- coiled spiral : these are the mother-cells of the anther ozoids. By comparing carefully-prepared and well-cut sections, the development of the antheridia and archegonia may be traced, and in both cases it may be seen that they originate from single superficial cells. In the case of the antheridia young stages of development are to be found on sections through the lateral and posterior parts of the prothallus, while young stages of development of the archegonia lie near to the organic apex. Young archegonia should also be observed from above in young pro- thalli mounted with the lower surface uppermost. If drawings be made of archegonia from both points of view, and of various ages, a comparison of them will give a clear idea of the processes of development. The dehiscence of the antheridia, the escape of the antherozoids, and their movements, should be observed with particular atten- tion in fresh prothalli mounted in water ; also the opening of the apex of the neck of the archegonia : in both cases the process depends upon a mucilaginous degeneration of cell-walls of the inner cells, and a subsequent swelling by taking up water, and consequent rupture of the outer walls. Further, the movements of the living antherozoids may be followed, and the act of fertilisation observed ; the antherozoids being arrested by the P 210 PRACTICAL BOTANY. mucilaginous mass projecting from the open archegonium, they pass through this and down the neck of the archegonium, and finally coalesce with the oosphere. C.TffE YOUNG SPOROPHORE, OR FERN PLANT. V. The result of the process of fertilisation of the oosphore of the archegonium by the antherozoids is the development of a new Fern plant, or Sporophore, and in cultures which have been continued for some months such young Fern plants may be clearly seen attached to the prothalli, but one prothallus produces only one young Fern plant. Select a prothallus to which a young Fern plant is thus attached, and wash from it the soil which adheres to it. Examine it with a lens, and observe 1. That the prothallus itself is similar in form and structure to those before observed. 2. That the young Fern plant is firmly attached to its under surface by a lateral protrusion (Foot). 3. That the young Fern plant consists of the following parts : A a. Root which turns downwards into the soil. A b. lateral protrusion, the Foot, which maintains a close physiological connection between the prothallus and the Fern plant. A c. first leaf, or Cotyledon, with an elongated petiole, and bifurcating, expanded, upper part: this usually grows upwards through the depression at the apex of the prothallus. d. Between the base of the cotyledon and the foot is the Apex of the stem, which continues its growth, and produces new leaves. MALE FERN. YOUNG SPOROPHORE. 211 Having thus gained a knowledge of the position of the several parts relatively to one another, and to the prothallus, in the case of a young Fern plant of considerable size, younger plants may successively be taken, and by a comparison of these the mode of development of the young embryo, or Fern plant, may be traced. In order to make preparations so as to show the several parts of the embryo, sections should be made either from fresh material, or better from material prepared with picric acid, and hardened in alcohol, as above directed for the prothalli. The direction of section should be parallel to the organic axis of the prothallus, and perpendicular to the flattened surfaces : in such sections, including embryos of suitable age, the stem, cotyledon, root, and foot may all be observed ; further, the origin of these several parts from definite segments of the fertilised oosphere may be traced. For details as to the sequence of cell-divisions in the first stages of development of the embryo reference should be made to Text-books. P2 0. EQUISETINE^S. EQUISETUM ARVENSE (The Common Horse- Tail). THE SPOROPHORE. The Vegetative Organs. I. Observe with the naked eye the following external characters in specimens of E. arvense which have been carefully dug up. N.B. The root-stock being a creeping one, and underground, it cannot be removed from the soil without injury by merely pulling it up : the specimens should be carefully dug up, so that the several parts may be seen in their natural position relatively to one another. 1. The external conformation of the Axial struc- tures or stems is the same whether they be creeping and underground, or erect and aerial : they consist of more or less elongated joints or Internodes, marked off from one another by Nodes, which may be recognised as the points of insertion of 2. The Leaf-sheaths, each of which surrounds the base of the interned e next above it, and splits at its upper limit into Teeth, the number of which varies on different axes. 3. The internodes are marked by projecting longitudinal Ridges, which may be traced upwards into the EQIHSETUM. SPOROPHORE. 213 leaf-sheath, and are then seen to be continuous to the apices of the teeth : between the ridges are depressed channels. 4. The Lateral branches are always inserted at the nodes, and at the base of the leaf-sheaths; note that they are arranged in whorls, and appear to burst through and rupture the leaf-sheath near to its point of insertion on the axis, and at points alternating with the projecting ridges, i.e., at the channels. 5. The Roots (to be clearly distinguished from the underground root-stock, which shows an alternation of nodes and internodes as above described), are thin and fibrous, and branch monopodially : they are inserted with a whorled arrangement at the nodes, immediately below the point of insertion of the lateral buds. The underground stems and the roots are covered externally by numerous fine root-hairs of a brown colour. 6. Note that at many of the nodes the lateral branches, or the roots, or both may be partially suppressed, their development being arrested at an early stage : also that frequently the basal internode of lateral shoots attached to the nodes of the root-stock may be much distended, while its apical bud is arrested : in some cases more than one internode may take part in this development, the result being a moniliform structure : the Tubers thus formed are reservoirs of reserve material, and being easily separated from the parent plant, they serve to propagate the plant by a purely vegetative process. Any node separated from the parent plant may also serve the same purpose under favourable circumstances. 7. Observe particularly that the teeth of each leaf- 214 PRACTICAL BOTANY. sheath correspond in position to the channels of the next higher internode ; since the teeth are continuous downwards with the ridges of the lower internode, it follows that the ridges of the lower internode alternate in position with those of the internode next above it. Strip off carefully one leaf-sheath, and it may then be clearly seen that the ridges of the upper internode alternate with those of the internode next below it. II. Cut transverse sections from a mature internode of an upright aerial stem : mount some in glycerine, others in Schulze's solution, and examine first with a low power : observe i. The sinuous outline of the section, the projections corresponding to the ridges observed externally with the naked eye, and the indentations to the channels intervening between them. ii. The section is limited at the periphery by an ill- defined layer of epidermis, which, together with sub- jacent tissues, forms a band of thick-walled tissue of very variable breadth ; thus the band is broad at the most convex parts of the ridges, and at the most depressed parts of the channels, while it is reduced on the sloping sides of the ridges to the single layer of thick-walled epidermal cells. iii. Beneath this is a broad band of Cortical tissue, in which may be recognised a. Groups of Chlorophyll-parenchyma of oval outline; one of these lies opposite to each of the ridges, and extends to points close below the surface of the sloping sides. 6. Parenchyma composed of rounded cells with little or no chlorophyll. EQUISETUM. SPOROPHORE. 215 c. Large Intercellular cavities, which alternate in position with the ridges, and are thus opposite the channels of the outer surface. iv. The cortex is limited internally by a single sinuous layer consisting of cells in close contact with one another ; this is the Bundle-sheath (see below) : it forms a continuous and sinuous ring surrounding v. The Vascular bundles, which may be recog- nised as oval groups of elements of smaller size than those of the surrounding tissue : they alternate in position with the intercellular cavities of the cortex, and are thus opposite to the ridges which project on the external surface. vi. The Pith, which lies centrally, consists of thinwalled tissue, and is in great part obliterated by a large central cavity. III. Before proceeding to the more minute study of these several tissues, cut transverse sections through a leaf-sheath : mount in glycerine, and examine with a low power. It may be observed that the arrangement of tissues is not unlike that of the peripheral tissues of the internode. Note especially that as in the internode, so also in the leaf-sheath, one vascular bundle (here of small size and simple structure), is to be found opposite each ridge. IV. Cut a series of rather thick transverse sections through the nodal region : it will be best to select one which bears no fully-developed, lateral branches. Keep them all in their right order of succession, mount, and compare them under a low power, starting from such a section above the node, as will show an arrangement of tissues typical of the internode, together 216 PKACTICAL BOTANY. with the leaf- sheath surrounding it. If these parts be in their natural position, it will be seen in this first section that the vascular bundles of the leaf- sheath alternate in position with those of the internodes. Passing the sections successively under observation, it will be seen that each bundle of the internode divides into two branches, which diverge and insert themselves respectively right and left on bundles of the leaf-sheath, at the point where these curve into the axis, and begin their downward course through the next internode. Thus the course of each bundle of the leaf-trace is simply this : it passes from the leaf-sheath into the axis, traverses one internode, and at the next lower node it forks, the branch bundles inserting themselves on bundles entering at that node. These facts, together with external observation of the ridges of the leaf-sheaths and internodes, will suffice for the construction of the whole bundle-system of the shoot of E. arvense, which is also typical of the whole group. The bundle-system may be actually demonstrated by dissection in the stem of one of the larger forms, viz., E. Telmateia. Take a fresh and well-grown shoot, and cut from the thickest part of it a piece about four inches in length, and including a node : then remove from it the outer tissues, and scrape the soft parenchyma away till the vascular bundles are laid bare ; then slit the hollow stem longitudinally, flatten it out, and carefully scrape away the softer tissues from the inside till the vascular bundles are clearly seen then treat for some hours with alcohol to remove the air ; bubbles from the intercellular spaces, and warm gently in weak solution of potash : the preparation may be preserved in glycerine, or in glycerine jelly. If such a preparation be carefully made it will show the course of the vascular bundles in the internode, as well as the branchings and fusions at the node. EQUISETUM. SPOROPHORE. 217 Returning to the study of the transverse sections of the internode, examine them under a high power, and observe 1. The superficial cells of irregular size and shape which form an ill-defined epidermis, many projecting as rounded excrescences beyond the general surface : their walls are thick, and show on the outer surface small and irregular projections : the cell-contents are scanty. Note that on the sloping sides of the ridges, and imme- diately above the chlorophyll-parenchyma, Stomata may be seen cut in section, and showing two Guard- cells which surround the pore, and two Subsidiary cells which fit closely round them : there is a large respiratory cavity beneath each stoma. 2. The sub-adjacent cells, composing with the epidermis the band of thick-walled tissue before men- tioned, have cellulose walls (blue with Schulze's solution), with narrow pits. 3. The cells of the Chlorophyll-parenchyma are thin-walled, and of oblong form : the chlorophyll granules are numerous and clearly marked. 4. The remnants of disorganised cells along the margins of the intercellular cavities, which show that they are of lysigenetic origin : the same may be observed with regard to the central cavity. Add a little caustic potash to the sections mounted in glycerine, and then observe the cells of the bundlesheath under a high power: their radial walls will be seen to show the characteristic dark dot-like appearance. Passing on to the Vascular bundles, their most marked constituents will be two to four groups of dark-looking elements, which are Tracheides 218 PRACTICAL BOTANY. of the Xylem, and are disposed, roughly speaking, in V the form of a V, while the apex of the is occupied in each bundle by a large air-cavity. There are origin- ally four groups of xylem elements in each bundle, two bordering on the cavity, and two nearer the bundle- sheath ; the elements of the former are often only im- perfectly seen in transverse sections, since they are apt to become disorganised during development. Between the air-cavity and the bundle-sheath lies a mass of tissue of the Phloem, with relatively thin cellulose walls ; Sieve-plates may sometimes be observed in surface view in this tissue. Y. Compare transverse sections of the underground axis, or root-stock, with those of the aerial axis : the sections may be prepared in the same way as the above. Note that 1. The superficial cells have brown walls, and often grow out as long, brown, root-hairs : there are no stomata. 2. The sub-jaccnt cortex is thin-walled, and colourless, and often contains much starch. 3. The ridges, intercellular cavities of the cortex, and vascular bundles have the same relative positions as in the aerial stem. 4. The structure of the vascular bundles is similar to that in the aerial axis. 5. There is no cavity at the centre of the axis. Cut transverse sections of one of the tubers ; treat with potash, and mount in glycerine. Observe 1. The brown-walled epidermis with many hairs, similar to those on the root-stock. A 2. sub-epidermal layer with thickened walls. EQUISETUM. SPOKOPHORE. 219 3. The bulky parenchyma with numerous starch grains : there are no large intercellular cavities as in the aerial axis. 4. Isolated vascular bundles, each of which is surrounded by a special bundle-sheath, quite distinct from that of the other bundles ; there is no general bundle-sheath as in the normal axes. A comparison of the stems of various species of Equisetum in respect of the bundle-sheath shows that there is some want of uniformity in its arrangement, even in the normal axes : further, it has been shown that such differences may occur between the rhizome and the aerial axis even in the same species. In E. arvense there is a difference in this respect between the tubers and other axes. VI. Make preparations suitable for the study of the epidermis in surface view, by cutting longitudinal, tan- gential sections, and treat as before, mounting with the outer surface uppermost : observe under a high power ,1. That the superficial cells covering the ridges are of elongated form, with smooth outer walls, and thickened, pitted, inner walls : there are no stomata on the ridges. 2. That the superficial cells of the grooves are shorter, and nearly square, their outer walls bearing those rounded excrescences already observed in trans- verse sections, while their whole surface is dotted with small projections : in this part are also numerous Stomata, which present the characteristic appearance of two concentric > circles, the outer being the limit of the two subsidiary cells, the inner that of the two guard-cells. Note also the peculiar radiate marking, which is due to irregularity of thickening of the wall separating the guard-cells from the subsidiary cells. Treat sections similar to the above with Schulze's macerating fluid + HN0 (KCl 3 3) for some hours, and then dry them with 220 PEACTICAL BOTANY. blotting-paper, and ignite them in a spirit lamp on platinum foil, or on a cover glass ; then treat the ash with weak acetic acid ; mount the residue, and examine under a high power : a skeleton will then be found to remain, which represents clearly the several details of structure of the epidermis above described. From the treatment which the preparation has undergone it may be concluded that this is a skeleton of silica. VII. Cut radial longitudinal sections of an internode of an underground stem : wash them well with water to remove as much as possible of the starch, and mount some of them in glycerine, others in Schulze's solution. Note successively the following tissues 1. The oblong superficial cells with brown walls, frequently bearing unicellular hairs. 2. The oblong cells of the Cortex with cellulose walls, and containing starch. 3. The Vascular bundles, which may be easily recognised as transparent bands of tissue, in which may be clearly seen a. The elongated Tracheides of the xylem, showing annular, spiral, or irregularly reticulate thickening of the walls : these thickenings stain yellow with Schulze's solution : there are no protoplasmic contents : the lignified rings are often found free in the intercellular cavities, owing to the rupture of the thinner parts of the walls : for this reason also the annular vessels, which adjoin the intercellular cavities in the bundles, are frequently not to be found in transverse sections. 1. The Phloem consisting of a. Sieve-tubes, which- are elongated elements, with cellulose walls, and granular protoplasmic contents, EQUISETUM. SPOROPHORE. 221 and are divided into joints by transverse or oblique walls: they correspond in general characters to the sieve-tubes of the higher plants, but the sieve-structure of the terminal walls is not clear. Numerous highly refractive granules are found on both sides of the terminal walls. ft. Cambiform cells of oblong form, with cellulose walls. VIII. From buds which have been hardened in alcohol cut median longitudinal sections : treat them for a short time with a strong solution of caustic potash, then wash them with water, and mount in strong acetic acid. Examine them first with a low power, and observe that the nodes and internodes are easily recognised in the lower, older parts of the sections: the former being the points of insertion of the leaf-sheaths, opposite which are various complications of the arrange- ment of the tissues as has already been observed; in the internodes the tissues show greater regularity of arrangement. Note that on passing towards the apex the internodes are successively shorter, and the character of the tissues of both nodes and internodes becomes more uniform also that the leaf-sheaths become suc; cessively shorter. Following the axis upwards it may be seen to terminate in a sharp cone, which is the pnnctum vegetationis, consisting of cells undergoing division, which constitute the primary meristem. Here and there it may be seen that lateral buds have been cut through, they are situated at the nodes, and appear to be completely surrounded by the tissues at the bases of the leaves; in their form and structure they resemble the punctum vegetationis of the main 222 PKACTICAL BOTANY. axis, but on a smaller scale. Note also the irregularly annular or spiral tracheides in the internodes, and the way in which their structure is modified at the nodes, where they appear shorter, and are more closely reticulated. Examine the punctum vegetationis under a high power, and observe 1. At the extreme apex a single, large, wedge-shaped cell ; this is the Apical cell. The cells immediately adjoining it are arranged in regular order, and are of definite form, being Segments successively cut off from the apical cell. Observe how the older segments, which are further from the apical cell, have been suc- cessively divided up by walls perpendicular to the outer surface (anticlinal), and parallel to the outer surface (periclinal). The details of arrangement of the suc- cessive walls may with advantage be traced by com- parison of several preparations, and explained by reference to the Text-Books. Since the superficial cells are subject to repeated periclinal divisions it is clear that there is no definite layer of dermatogen : compare this structure of the punctum vegetationis with that of the lateral buds above mentioned. 2. Note the leaf-sheaths, successively smaller towards the extreme apex, and observe how they originate by outgrowth and division of successive zones of cells below the apex. 3. Attention should also be paid to the mode of origin of the lateral buds : a diligent comparison of them in various stages of development will show that they are not of endogenous origin, but are derived from superficial cells lying immediately above the insertions EQUISETUM. SPOROPHORE. 223 of the leaf-sheaths. These cells divide, and form the young buds, which subsequently appear to be completely embedded in the tissue of the leaf-sheath, and ultimately burst through it. 4. It will be useful further to trace the development of the several tissues, and to note their relations to-the apical cell and its segments. IX. Cut a series of transverse sections through a bud : prepare and mount them as above directed (VIII), being careful to keep them in their proper order of succession, and with their upper side uppermost. Some of the sections will only have passed through the upper parts of the leaf-sheaths, which will appear as concentric rings, with a structure similar to that already observed (III.) : note that the leaves of successive whorls alternate one with another. In the centre of these rings there will be found in each of the lower sections of the series a transverse section of the axis, and one of the sections should include the punctum vegetationis, which would thus be seen from above. In this preparation observe that the apical cell appears of triangular outline, while the segments are arranged regularly around it : from this observation, and from its appearance in the longitudinal section, it may be concluded that the apical cell has the form of a threesided pyramid, and that segments are cut off from three- sides. From the observation of transverse sections cutting the axis below the apical cell, and a comparison of these results with those drawn from a study of longitudinal sections, the mode of subdivision of the segments should be fully made out. X. Cut transverse sections of a well-developed root 224 PRACTICAL BOTANY. of E. arvense, treat them with potash, and mount in glycerine : examine them under a high power, and observe 1. That there is a peripheral band of tissue with dark brown walls : single superficial cells have grown out. as root-hairs. 2. Then follows a broad band of colourless Cortex, with large intercellular spaces ; this is limited internally by- A 3. definite layer of cells having the well-marked characteristics of the Bundle-sheath : 4. Within this is the Phloem-sheath, the cells of which are opposite to those of the bundle-sheath, and are derived with the latter from the inmost layer of the cortex. This surrounds 5. The vascular cylinder, consisting of a. Four Xylem groups, each of which may consist of only one tracheide, while one large element often occupies a central position. I. The spaces between these are occupied by illdefined groups of Phloem, and Conjunctive parenchyma. The arrangement of tissues at the apex of the root of Equisetum may be studied in the same way as above described for the root of Aspidium Filix-Mas, and it will be found to be similar to it in all the more important points. Attention should also be paid to the mode of origin of the lateral roots, which here spring from the phloem-sheath, while in Ferns they arise from cells of the bundle-sheath. The Sporangia. XI. Examine one of the fertile stems, which rise above ground in the spring, with the naked eye ; ob- EQUISETUM. SPORANGIA. 225 serve that the internodes and leaf-sheaths of the lower part of it are similar to those of the vegetative axes. Passing upwards, note that the last leaf-sheath below the spike is of smaller size than the rest. The spike itself is covered by closely-arranged peltate scales, of hexagonal outline as seen from without : these are arranged in more or less regular whorls. Remove some of the scales, and examine one of them in detail: it consists of a thin pedicel by which it is attached to the axis ; the pedicel widens out towards its apex into a flattened shield-like structure, from the lower surface of which a number of sacs (Sporangia) are suspended. XII. Cut transverse sections through a spike, so as to include some of the scales : mount in glycerine, and observe under a low power. There will be seen a bulky Pith, a ring of Vascular bundles, and a band of cortex. The Pedicels will appear extending radially from the axis, and widening at the outer limit into the peltate expansion, on the lower surface of which two sac-like Sporangia may be seen. Note that a vascular bundle runs up the pedicel, and ramifies in the peltate expansion. Examine one of the sporangia under a high power, and note a. The Wall which is one layer of cells in thickness : the walls of these cells are strengthened by a spiral or annular thickening : the wall ruptures by a longitudinal slit on the side next the pedicel. b. Many Spores may be found in the sporangia, or scattered through the glycerine : examine them care- fully, and observe the spirally-coiled Elaters, and the Q 226 PRACTICAL BOTANY. smooth inner coats of the spore, which inclose a protoplasmic body with a well-marked nucleus. Scatter fresh spores upon a slide, and breathe upon them gently ; then observe them under the microscope : the elaters will be seen to execute active movements, thus showing that they are hygroscopic. By cutting transverse sections of spikes of various stages of development, which have been hardened in alcohol, or in picric acid and then in alcohol, mounting them in glycerine, and comparing them, the history of the development of the sporangium may be traced. The chief points to be observed will be (1) that A the sporangia appear as multicellular protuberances. (2) single hypodermal cell, the archesporium, gives rise by division to the spore-mother-cells, while the superficial layer of cells which covers the archesporium divides into three, of which the outermost alone remains as the wall of the mature sporangium. (3) Each of the spore-mother-cells divides into four cells, which develop further into mature spores. THE OOPHORE. The fresh spores may be sown on moist soil, and the first stages of germination, which are rapid, may be easily observed ; the later stages are, however, slow, and to see these the cultures must be carefully kept. The result is the formation of prothalli (oophores) of irregular form, some of which produce antheridia after five to six weeks. Other prothalli of larger size produce archegonia after about two to three months. The antheridia are embedded in the tissue of the prothallus, and produce large antherozoids. The archegonia are borne on the upper surface. The result of fertilisation of the egg- cell of the archegonium is the formation of an embryo, which develops as the spore-bearing plant or sporophore. Endeavours should be made to obtain healthy cultures of the prothalli of Equisetum in which the above and other points described in other Text-books may be observed. END OF PART I. MESSRS. MACMILLAN AND CO.'S MANUALS FOR STUDENTS. THE STUDENT'S FLORA OF THE BRITISH ISLANDS. By Sir J. D. HOOKER, K.C.S.I., C.B., M.D., F.R.S.. D.C.L Globe 8vo 10s. 6d. STRUCTURAL BOTANY, OR ORGANOGRAPHY ON THE BASIS OF MORPHOLOGY. To which are added the principles of Taxonomy and Phytography, and a Glossary of Botanical Terms. By Professor ASA GRAY, LL.D. 8vo. 10. Qd. A COURSE OF INSTRUCTION IN ZOOTOMY (VERTEBRATA). By T. JEFFREY PARKER, B.Sc. With Illustrations. Crown 8vo. 8s. 6d. AGRICULTURAL CHEMICAL ANALYSIS. A Handbook of. By PERCY FARADAY FRANKLAND, Ph.D., B.Sc., F.C.S. 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