Part III

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 punctwm vegetationis, which would thus be seen from above. In this preparation observe that the apical cell appears of triangular outline (compare Fig. 13), 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 three-sided 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 of E. arvense: treat them with potash, and mount i n 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 byA 3. definite layer of cells having the well-marked characteristics of the endodermis. 4. Within this is the pericycle, the cells of which are opposite to those of the endodermis, and are derived with the latter from the inmost layer of the cortex. This surrounds z 338 PRACTICAL BOTANY 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. 6. The space intervening in each bundle between these four groups of xylem is occupied by an ill-defined group of phloem, and conjunctive parenchyma. The arrangement of tissues at the apex of the root of Eguisetum 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 pericycle, while in Ferns they arise from cells of the endodermis. The Sporangia XI. Examine with the naked eye one of the palecoloured, fertile stems, which rise above ground before the green vegetative shoots in the spring : observe 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. EQUISETUM SPOROPHYTE 339 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. I. Many spores may be found in the sporangia, or scattered through the glycerine : examine them carefully, and observe the spirally-coiled elaters, and the 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 highly sensitive to changes of moisture in the air. 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 the sporangia appear as multicellular protuberances ; (2) that a z2 340 PRACTICAL BOTANY 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) that each of the spore-mother-cells divides into four cells, which develop further into mature spores. THE GAMETOPHYTE, OR OOPHYTE 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 (oophoytes) of irregular form, some of which produce antheridia after five to six weeks. Other prothalli, of larger size and more complicated form, produce archegonia after about two to three months. The antheridia are embedded in the tissue of the pro- thallus, and produce large spermatozoids. The archegonia are borne on the upper surface, and correspond in structure to those of the Ferns. The result of fertilization of the ovum of the archegonium is the formation of an embryo, which develops as the spore-bearing plant or sporophyte. Endeavours should be made to obtain healthy cultures of the prothalli of Equisetum, in which the above and other points may be observed. BRYOPHYTA A. MUSCI POLYTRICHUM COMMUNE, L A. GENERAL EXTERNAL CHARACTERS I. Observe in well-grown specimens of this Moss taken in spring or early summer 1. The erect stem, 1 which may attain a considerable length, branching but rarely : 2. The 1 leaves, of relatively small size, and simple form ; their arrangement is on a complicated plan (see p. 344) : at the base of the stem note A 3. dense mat of rhizoids of brownish colour. At the apex of some specimens will be found merely a bud, composed of young leaves of the vegetative type ; other specimens will bear at their apex< 4. Perigonia, or perichaetia ; cup-like rosettes of leaves, which assume a bright reddish or orange colour, and protect the antheridia ; other specimens again may bear at their apex 1 Though the terms " stem " and " leaf " are used here, it must be distinctly borne in mind that the members thus named, being parts of the oophyte generation are not homologous with, but at most only analogous to the stem and leaf in vascular plants, which are parts of the sporophyte generation, '342 PRACTICAL BOTANY 5. The mature sporogonium or spore-capsule, of which the head or theca is supported on a long stalk, or seta. Note in specimens which are not too ripe a. The calyptra, a dry fibrous hood, covering the apex of the sporogonium : beneath this is I. The lid-like operculum with its terminal beak : this lid may be easily detached, disclosing c. The pale-grey epiphragm, which appears as a transverse membrane, attached at its margin to the capsule by a number of short teeth of the peristome. d. At the base of the theca observe a swelling called the apophysis. e. By carefully removing the leaves from the apex of a plant which bears a sporogonium, it may be seen that the base of the seta is enveloped by a closely fitting sheath, the veil or vaginula, the origin of which will be explained later (page 350). Observation of the external characters of a simpler Moss, e.g. Funaria hygrometrica, will give in the main similar results to those above described for the larger Polytrichum. E. MICROSCOPIC INVESTIGATION Oophyte Generation II. Cut transverse sections of a mature stem of Polytrichum : mount some in glycerine, others in chlor-zinc-iodine or in iodine solution : examine them first under a low power, and observe in those mounted in glycerine 1. The outline of the section, which is usually more or less clearly triangular. POLYTRICHUM OOPHYTE GENERATION 343 2. The dense reddish-brown band of peripheral sclerenchyma, which passes over gradually into A 3. broad, thinner-walled band of tissue, which may be termed the cortex : this finally surrounds A 4. central mass of firm, yellow- walled tissue. Examine these several tissues in detail, under a high power, and observe that 1. At the extreme outer limit is a thin cuticle, with small and irregular outgrowths : there is no clearly defined epidermal layer. 2. The peripheral sclerenchyma consists of cells with clearly stratified red walls, which are of such thickness as almost to obliterate the cell-cavity. 3. The broad band of tissue of the cortex has relatively thin, yellowish or colourless walls, and protoplasmic contents with starch-granules, and globules of oil (compare sections treated with iodine). 4. The central mass of tissue (which may be com- pared to a vascular bundle) is not sharply limited from the cortex : it consists of A a. peripheral, small-celled, and thin-walled portion, the walls of which do not stain blue, but light yellow with Schulze's solution. A I. central, thick-walled part, without cell- contents : the thick walls stain dark brown with Schulze's solution : the elements are often divided by delicate septa, which are not stained by Schulze's solution. This tissue may be compared to the xylem of true vascular plants. Here and there small groups of tissues similar to the above may be seen in the cortex ; these are the strands 344 PRACTICAL BOTANY which enter the stem from the leaves, and pass inwards towards the central bundle. III. Cut median longitudinal sections of the mature stem of Polytrichum : mount as before, and note that the peripheral sclerenchyma consists of elongated prosenchymatous elements, while the cells of the massive cortex are of a parenchymatous form. The elements of the central strand are elongated, and their lateral walls smooth, without pits : they are separated one from another by thin oblique septa. Observe that where the median plane of a leaf has been cut through longitudinally, a strand of tissues similar to those constituting the central strand may be traced, passing obliquely through the cortex towards the central strand. By cutting transverse and longitudinal sections of the apex of the stem of Polytrichum^ or Fwwria, it may be ascertained that there is in each case a single apical cell of tetrahedral form, that segments are cut off successively from the three sides, and that one leaf originates from each segment : in the transverse sections it may, however, he seen that in both plants the angle of divergence between the successive leaves (and similarly between the successive segments) is larger than one-third : thus the leaves form three parastichies, and this will account for the apparent complexity of their arrangement in these plants. In Fissldem the arrangement is in two longitudinal rows or orthostichies, and there is a bilateral wedge-shaped apical cell. In Fontinalis there is a tetrahedral apical cell, but the divergence of both segments and leaves is one-third. IV. Strip off a few mature leaves : mount one of them in water, with the upper surface uppermost, and observe under a low power that the narrow, linear upper portion is marked on its upper surface by longitudinal striae (the lamellae), and has a minutely POLYTRICHUM OOPHYTE GENERATION 345 serrated margin : the basal portion of the leaf, which is closely applied to the stem, is broad, but thin and membranous, and is not marked by longitudinal strise. V. Cut transverse sections of leaves : this may easily be done by holding the terminal bud of a mature plant between pieces of pith, or by embedding in paraffin, and then cutting transverse sections of the whole bud. Mount all the sections as before, and examine first with a low power. Neglecting the almost circular transverse sections of the stem, recognize 1. Those transverse sections which have passed through the sheathing basal portions of the leaves : these may be readily distinguished by their broad lateral wings, only one layer of cells in thickness. 2. Those which have been taken from the upper part of the leaf: these maybe distinguished by their more bulky appearance. Having recognized these sections, put on a high power and examine them in detail : 1. In the section of the sheathing base of the leaf observe a. The two lateral wings, consisting of a single layer of cells, with thickened outer walls, and but little chlorophyll. b. The more bulky central portion consisting of An i. irregular layer of superficial cells with thickened outer walls, covering both upper and lower surface : beneath these are ii. Bands of sclerenchyma, in which the lumen is almost obliterated. iii. Within these lies a " vascular bundle " consisting 346 PRACTICAL BOTANY of elements essentially similar to those composing the central bundle of the stem. 2. In the sections of the upper part of the leaf note that the arrangement of the tissues is for the most part similar to that in the above sections, but rather more bulky, while opposite each of the cells at the upper surface is seen to be attached a series of three to six chlorophyll-containing cells, which represent transverse sections of those longitudinal plates or lamellae above observed on the upper surface of the leaf, under a low power ; the uppermost cell in each lamella (as seen in section) is enlarged and forked. It is obvious that these chlorophyll-containing lamellse are separate laterally from one another : they constitute the chief assimilating tissue of the plant. For comparison with the above, a Moss of simpler type may be taken, e. g. Funaria hygrometrica. As before there is an erect stem, with a mat of brown rhizoids at its base : it bears a number of leaves of somewhat variable form, more or less widely ovato- lanceolate. Mount a single leaf in water and examine under a low power : note the clearly marked midrib, terminating in the acuminate apex, the thin lateral portions, consisting of only a single layer of cells containing chlorophyll, and bounded by an entire margin. Cut transverse sections of the stem, and mount in weak glycerine or glycerine jelly : on examination under a low power it will be seen that the stem is of much simpler structure than that of Polytrichum : the peripheral tissues have brown walls, but they are not thickened to any marked degree : at the centre is a strand of thin-walled, small-celled tissue : the peripheral tissues usually contain chlorophyll. POLYTRICHUM SEXUAL ORGANS 347 Sexual Organs VI. Take a mature antheridium-bearing axis of PolytTiclium, and dissect it with needles in a watchglass, keeping all the detached parts. Examine them carefully with a lens, and observe the following categories of organs 1. The perigonial leaves, which are widened laterally into very broad membranous wings, with a clearly defined, central midrib. 2. The white, club-shaped antheridia. 3. The paraphyses, which will often associated with the antheridia : some of be found them are simply filamentous, others are more or less clearly spathulate. VII. Cut median longitudinal sections ot a male axis : mount in weak glycerine, and with a low power recognize the several organs above described, and their relative positions : note especially the antheridia in the axils of the perigonial leaves. Observe under a high power the structure of a single antheridium : it consists of a short stalk, and a club-shaped body, composed of (i.) a -wall a single layer of cells in thickness, and (ii.) a central mass of cells of more or less clearly cubical form : these are the spermatocytes or mother- cells of the spermatozoids. VIII. Take fresh antheridium-bearing specimens of Polytriclmm, after some days of dry weather (or keep them rather dry for some days, carefully preventing any access of water from above) : squeeze one of them between the finger and thumb : the antheridia will 348 PRACTICAL BOTANY thus be easily forced from their position, and may be mounted in water. If they were properly mature, it may then be seen that on contact with water the antheridia burst, and the spermatocytes escape, aggregated in a mass. In each cell of this mass a spiral filament may be seen, in active movement : it may be seen to escape ultimately, owing to mucilagin- ous swelling of the wall of the mother-cell, as a free spermatozoid of spiral form, having two cilia. Antheridia may be obtained on Funaria hygrometrica at almost any period of the year : they are borne on special branches as in Polytrichum, but are surrounded by a less conspicuous perigonium : these axes are usually shorter than those which bear the female organs. IX. Take a sod of Funaria 1 with no sporogonia as yet visible upon it, but which bears antheridia : these will be situated at the apices of the shorter axes : many of the longer axes will appear to be terminated by ordinary vegetative leaves, and it is on these axes that the archegonia may be found. From such buds, after hardening in alcohol, cut median longitudinal sections : if not transparent enough treat with dilute potash solution, and mount in weak 1 Since Funaria hygrometrica produces sporogonia at all times of the year, and is very common, while Polytrichum commune is reproduced sexually only in the spring and early summer, it will be convenient in most cases to use the former in examining the archegonia. In either case, however, it is a matter of some experience and expenditure of time to get a good series of preparations illustrating the development and structure of the archegonium, and the early stages of the production of the sporogonium. Various other Mosses might be used for the purpose of this work, especially such as grow in tufts, and produce their sporogonia almost simultaneously. or TH UNIVF. POLYTRICHUM SEXUAL ORGANS 349 glycerine : subsequently the sections may be transferred to glycerine jelly. Examine first with a low power, when the usual arrangement of axis and leaves may be observed ; between the youngest leaves an archegonium (or several) may sometimes be detected. If mature, it will be seen to be a flask-shaped organ, seated on a short massive stalk : it consists of 1. An elongated neck, more or less contorted, com- posed of a single layer of cells arranged in four to six rows : these surround a central canal, which is filled with mucilage at the time of fertilization, but before maturity there may be seen within it a series of canal cells. A 2. lower, enlarged ventral portion, consisting of two layers of cells, which constitute the wall, and inclose a central space, in which may be seen the naked spherical oosphere or ovum, and above it (up to the period of maturity) the smaller ventral canal cell. The process of fertilization cannot readily be observed in Mosses. Similar sections, similarly prepared from rather older speci- mens, may show as the first results of fertilization that the neck of the archegonium turns brown and withers, while the wall of the ventral portion and the stalk show considerable increase in bulk, and frequent cell- divisions. Meanwhile growth and celldivision take place also in the fertilised ovum, resulting ultimately in the development of the sporogonium : the growth of the wall of the archegonium keeps pace for some time with that of the young sporogonium, completely inclosing it, but as it increases towards maturity, the wall of the archegonium is ruptured transversely about half-way up : the apical part is carried upward by the growing sporogonium, as the calyptra which covers 350 PRACTICAL BOTANY its apex, while the lower portion remains as an investment of the base of the seta, and is called the veil or vaginula. Note especially in young sporogonia the two-sided, wedgeshaped apical cell, with segments cut off from either side. Sporophyte Generation The Sporogonium X. Having noted the external characters of the sporogonium of Polytrichum, as above described, cut transverse sections of the mature seta : mount in glycerine or glycerine jelly. Being a cylindrical organ the transverse section is circular. Note 1. The superficial layer of cells with a definite cuticle and thick yellow walls. A 2. band of brown sclerenchyma, which graduates internally into A 3. thin-walled parenchyma, with large inter- cellular spaces, and containing chlorophyll. 4. Centrally is a strand of denser tissue without intercellular spaces. XI. Cut median longitudinal sections of the base of the seta, which is inserted on the apex of the Moss-plant or oophyte : mount as before, and note in the upper part of the seta the superficial layer, brown scleren- chyma, thin-walled parenchyma, and central strand, as above described. Following the seta down to the base, it will be seen that the cuticle and brown sclerenchyma stop short, and are replaced by thin-walled parenchyma with plentiful protoplasm ; this tissue of the sporophyte is in close connection with the inner surface of the POLYTR1CHUM THE SPOROGONIUM 351 vaginula, which belongs to the oophyte generation. With this close physiological connection of the sporophyte and oophyte in the Moss, compare the connection by means of the foot in Ferns. Similar sections may be prepared, with similar results, from plants of Funaria, but there will be greater difficulty in this case, owing to the smaller size of this Moss. XII. Passing now to the apex of the sporogonium of Polytrichum, remove the calyptra : mount it in water or weak glycerine, and examine under a low power. It consists of dry, often branched, hypha-like filaments, loosely matted together : the neck of the archegonium may often be recognized at its extreme apex. The calyptra of Funaria may be treated in a similar way : here the brown neck of the archegonium is clearly seen, while the body of the calyptra consists of a con- tinuous tissue, a single layer of cells in thickness. XIII. It will be found convenient to take first the capsule of one of the simpler Mosses, e.g. Funaria. and subsequently to proceed to a more complicated example, e.g. Polytrichum. After noting the oval form, and the obliquely placed operculum, embed capsules of Funaria, which have been hardened in alcohol, in paraffin : cut median longitudinal sections : mount in glycerine or in glycerine jelly, and examine first with a low power. N.B. It will be well to select young capsules of such age that the peristome (seen through the operculum) shall show a pale yellow tinge : later it assumes a dark yellow or orange colour, and 352 PKACTICAL BOTANY in such cases the spores would be almost mature : the structure of the whole capsule would accordingly be more difficult to understand than in the younger specimens. Observe 1. The seta, which widens out gradually into 2. The theca or capsule, without any clearly marked basal swelling, or apophysis : at the apex of the theca observe that the section has traversed 3. The operculum or dome-like lid : beneath this 4. The yellow or orange peristome : in the lower part of the capsule note 5. The outer wall consisting of a clearly marked epidermis, and beneath