Part II

macrosporangia) . APOGAMY. In some Fern.s (Pteris cretica ; Aspidium filix mas, var. cristatum; A.falcatum; Todea africana) the young plant is not developed as a consequence of fertilisation, but as a bud from the protballium. This is known as apogamy, or loss of the power of sexual reproduction. The antheridia are generally more or less developed ; archegonia are entirely wanting in Asp. filix mas, var. 204 PTERIDOPHYTA. cristatum. This variety has probably only become apogamous through cultiva- tion. Many specimens of Isoetes lacustris, in a lake in the Vosges mountains, produce in the place where the sporangia are usually found, a vegetative shoot which grows into a new plant, so that the sexual generation is wanting in this case. Some specimens have sporangia on some leaves, and shoots on others. Apospory, or the formation of prothallia instead of sporangia and spores on the leaves, is found in Athyrium fdix femina, var. clarissimum. In this case the development of the sporangia proceeds only to a certain point, and from these arrested sporangia the prothallia are produced. Normal sporangia are entirely wanting in this variety, and in Aspidium angulare, var. pulcherrimum, sporangia are completely wanting. Compare the Mosses (page 188). The Vascular Cryptogams are divided into three large classes, in each of which a progressive development can be traced from the isosporous to the heterosporous forms, but some of these are now only known as fossils. Class 1. Filicinae (Ferns). The stem is small in comparison with the leaves, and branches only seldom, and then by lateral shoots. The leaves are scattered, large, often deeply divided, and of various highly developed forms. The undeveloped leaves are j-olled up in the bud, having what is termed circinate venation. The sporangia are situated on the edge or on the lower side of the leaves, those on which the sporangia are borne (sporophylls) being often the ordinary foliage-leaves ; but in a few cases the fertile differ from the barren ones (a higher stage in development). The fertile leaves are not confined to definite parts of the shoot, and do not limit its growth. The archesporium is most frequently -unicellular. A. Isosporous: Sub-Class 1. Filices (True Ferns). B. Heterosporous : Sub-Class 2. Hydropteridese (Water Ferns). Class 2. Equisetinae (Horsetails), in its widest meaning. The leaves in this class are small in comparison with the stem. They are arranged in whorls, and unite to form a sheath. The sporangia are situated on specially modified, shield-like leaves, which are closely packed together and form a " cone." The cone is borne terminally, and limits the growth of the shoot. The sporangia are developed from a large group of epidermal cells, the archesporium being unicellular. The branches are arranged in whorls, and develope acropetally. A. Isosporous: Sub-Class 1. Equisetaceae. Existing forms. B. Heterosporous : Sub-Class 2, Extinct forms. PTERIDOPHYTA. 205 Class 3. Lycopodinae (Club-Mosses). Roots generally branching dichotomously. The leaves are scattered or opposite, and in proportion to the stem very small, undivided, and simple. They are scale-like and triangular, tapering from a broad base to a point. The sporangia are situated singly (except in Psilotacece), and almost in every case on the upper side of the leaf or in the axil of a leaf ; but in some cases they are borne on the stem, just above the leaf-axil. The sporangia arise from groups of epidermal cells. The sporophylls are often modified, and differ from the foliage-leaves ; they are then arranged in cones placed terminally on branches, thus limiting their growth. A. Isosporous : Sub-Class 1. Lycopodieae. B. Heterosporous : Sub-Class 2. Selaginelleas. Class i. Filicinae (Ferns). The characteristics of this class have already been given on page -204. The class is divided into two sub-classes : 1. The TRUE FERNS, FILICES, have one kind of spore which generally developes monoecious prothallia, relatively large and green. The sporangia are most frequently situated in groups (sort), which are often covered but not enclosed by an indusium. 2. WATER FERNS, HYDROPTERIDE^E, have microsporangia with many (4 x 16) microspores, and macrosporanyia, each with one macrospore. The prothallium is small, and projects but slightly from the germinating spore. The sporangia are situated in groups (soH), which are either enclosed by an indusium, or enveloped in a portion of a leaf, to form " fruits " termed sporocarps. The old name for the Hydropteridese, "Khizocarpeae," i.e. the " root-fruited," originated from the erroneous supposition that the sporocarps were borne on the roots. Sub-Class 1. Filices (the True Ferns). Of the eight orders (with about 4,000 species) comprised in this sub-class, the Polypodiaceee is the largest (having about 2,800 species) and the most familiar ; for this reason it will be taken as typical. The sexual generation. When the spore germinates, the external covering (exospore) is ruptured, as in the Mosses. The internal cell-wall (endospore) grows out as a filament, which soon divides and gives rise to the prothallium, a flat, cellular expansion resembling the thallus of a Liverwort. In its fully developed state 206 PTER1DOPHYTA. the prothallium is generally heart-shaped, dark green, and pro- vided with root-hairs, and it attains a diameter of about one centimetre (Fig. 205). It is formed of one layer of cells, except along the central line near the anterior depression, where it becomes several layers of cells in thickness, forming the " cushion," on the lower side of which the archegonia are developed. The antheridia are first formed ; they are thus found on the oldest parts of the prothallium, on its edge, or among the w' root-hairs. The archegonia are developed FIG. 205. Prothallium (pp) of Maiden hair (Adiantum capillus veneris) with a young plant attached : b first leaf ; w' primary root ; w" adventitious roots ; h h root-hairs of the prothallium ( x abt. 30). later, and are therefore found near the apex. Several tropical Ferns have prothallia 1 deviating from this typical form; Trichomanes (Order HymenopJiyllacece) has filamentous, branched prothallia, which resemble the protonema of a Moss. Others, again, have strap-shaped prothallia, which resemble the thallus of certain Liverworts. FIG. 203. Antheridia of Maiden-hair (x 550). A Unripe; B ripe, but unopened ; Copen and ejecting the spermatozoids (s). Those which have been last ejected are still lying enclosed in their mother-cells, the others are coiled up and drag with them the cytoplasmic remains (b) ; /cells of the prothallium. 1 In the Polypodiaceas unisexual prothallia as distinct as those of Equisetum are of common occurrence. PTERIDOPHYTA. 207 The ARCHEGONIA have been already mentioned (p. 199, Fig. 201). The ANTHERIDIA are hemispherical or slightly conical bodies (Fig. 206). They consist, as in the Mosses, of a wall formed by one layer of cells, which encloses a number of spermatozoid-mothercells (A and B). The antheridia when ripe absorb water, and are ruptured, and the spirally-coiled spermatozoids liberated (Fig. 206 S). The spermatozoids have been observed to pass down the neck of the archegonium, and to fuse with the oosphere. The asexual generation. The first leaf, the "cotyledon," of the embryo developed from the oospore (Figs. 202, 205) is always small, and has a very simple shape. The leaves which occur later become more perfect, stage by stage, until the permanent form of leaf has been attained. The STEM is most frequently a subterranean or a semi-aerial rhizome ; it is only in the tropical, palm-like Tree-Ferns, that the stem raises itself high in the air and resembles that of a tree, with leaf-scars or with the remains of leaves attached (Figs. 207, 203) ; in certain species the stem is en- cased in a thick mat of aerial roots (Dicksonia antarctica). When the rhizome is horizontal the internodes are frequently elongated, and the leaves are arranged in two rows, as in Polypodium vulgare and in the Bracken-Fern (Pteridium aquilinum), etc. ; it is also generally dorsiventral, having a dorsal side on which the leaves are situated, and a ventral side, different from the former, on which the roots are borne. When the stem ascends in an oblique direc- tion, or is nearly vertical, its internodes are extremely short, and the leaves are arranged in a spiral line with a complicated phyllo- taxis, e.g. in Athyrium filix-fcemina, Aspidium filix-mas, etc. The BRANCHING upon the whole is extremely slight, and is generally confined to the petiole (e.g. Aspid. filix-mas) , or to the stem near the insertion of the leaves. Several species normally form buds on different parts of the lamina. The buds which are formed on the stem are not confined to the leaf-axil as in the higher plants. The Tree-Ferris, generally, do not branch at all. The VASCULAR BUNDLES are concentric, with the wood surrounded by the soft bast. In tranverse section they are seen as circles or irregularly-shaped figures (Fig. 203), the name of " King Charles and the Oak" (Bracken-Fern) having originated from the appear- ance which the bundles present in oblique section. In Osmunda they are collateral and resemble those of the Flowering-plants. Round each individual bundle is often a sheath of thick- walled, hard, brown, sclerenchymatous cells, which act as a mechanical w. B. P 208 PTERIDOPHYTA. tissue ; similar strands are also found in other parts of the stem. The LEAVES in nearly all species are only foliage-leaves, borne FIG. 207. Various Ferns (1, 2, 3, 4). in a spiral. They have an apical growth which continues for a long time, and some require several years for their complete development. In the buds they are rolled up (circinate) ; not only the midrib, but also all the lateral veins, and even the terminal PTEEIDOPHYTA. 209 portions of a leaf are sometimes rolled up together, the tissues of the leaf being already fully developed and only waiting to expand. The leaves are often excessively divided and compound,- with pinnate branches, and have an epidermis with stomata and a welldeveloped system of venation. Stipules are only found in Marattiacece and Opliioglossacece. Very often peculiar hairs or scales (palece, ramenta), dry, brown, flat and broad, are found on stem and leaf. The SPORANGIA are small, round capsules, which, in a very large number of Ferns, are formed on the back, but more rarely on the edge of the ordinary foliage-leaves. It is very seldom that there is any difference in form between the barren foliage-leaves and the fertile leaves, as is found for example in Blechnum spicant or Struthiopteris ; or that the fertile part of the leaf is differently constructed from the barren portion of the same leaf, as in the Royal-Fern (Osmunda). In such instances the mesophyll of the fertile parts is poorly developed. The sporangia in the Polypodiacece are lens-shaped, with long stalk (Fig. 211 D) : their wall consists of one cell-layer on which a single row of cells, passing vertically over the top (that is along the edge of the sporangium), is developed into the "ring" (annulus). The cells of the annulus are very much thickened on the inner and side walls, and are yellowish-brown. The thickened cells, however, do not entirely encircle the sporangium, and on one side, near the stalk, they pass over into large, flat, thin-walled cells. These form a weak point in the wall, and it is here that the sporangium is opened diagonally by the elongation of the annulus. The sporangium of the Polypodiacese opens as it dries. The cells of the annulus are very hygroscopic, and in straightening, the annulus bends back with a jerk, thus ejecting the spores to considerable distances. The cells of the annulus absorb water with great readiness. [The sporangium arises as a single epidermal cell, from which a basal stalk-cell is cut off. Three oblique cell-walls, intersecting near the base, are next formed in the upper cell, and a fourth between these and parallel to the free surface ; an inner tetrahedral cell enclosed by four others is thus formed, the outer cells become the wall of the sporangium, while the inner cell, by a series of walls, parallel to its sides, cuts off a layer of cells which eventually form the tapetum, the remaining central cell constituting the archesporium.] The SPORES are either oblong and bilateral, or they are tetra- 210 PTERIDOPHYTA. hedric with curved sides, depending upon the way in which the tetrad division has taken place. The sporangia are almost always situated on the nerves and gathered into groups, sort, which differ in form in the various- genera. The sori, in many genera, may be covered by a scale-like- structure, the indusium (Figs. 211 B, 212). In the majority of cases, each sorus is situated on a small papilla (placenta, or receptacle), which is supplied by a small vascu- lar bundle. Between the sporangia, hairs (paraphyses) are often situated, which spring either from the placenta or from the stalks of the sporangia. Systematic Division. The Ferns may be divided into-two- groups, characterized by the structure and development of the- sporangia. The sporangia in the EUSPORANGIAT^E take their origin from a group of epidermal cells, and their walls are formed by several layers of cells. The archesporium is the (not tetrahedric) hypodermal terminal cell of the axial row of cells which give rise- to the sporangium. In the LEPTOSPORANGIAT.E the sporangia are developed from single epidermal cells, and their walls are uni- layered. The archesporium is a central, often tetrahedric cell,, from which sixteen spore-mother-cells are 1 developed. It is diffi- cult to say which form is the oldest (according to Prantl, those- which have the sori on the nerve-endings) ; however, the Eusporan- giatise would seem to have made their appearance long before the others, and also well denned Marattiaceae and Ophioglos&acese- occur in the Kulm and Coal period, before the true Polypodiaceae. About 4,000 species of Ferns are now existing, and they are-- found especially in tropical and sub-tropical forests, Family 1. Eusporangiatae. Order 1. Ophioglossaceae. The prothallium differs from that of all other Ferns in being subterranean, free from chlorophyll,, pale and tuberous. The stem is extremely short, with short internodes, most frequently unbranched, vertical, and entirely buried in the ground (Fig. 208 st}. In several species (among which are the native ones) one leaf is produced every year, which has taken three to four years for its development. In Botry- chium a closed, sheath-like basal part of each leaf cover's the sub- sequent leaves during their development. In Ophioglossum and 1 The position of the annulus varies in the different orders ; longitudinal in Polypodiaceae, Hymenophyllaceaa, and Cyatheacese ; transverse in Schizaa- acese, Gleicheniacese : indistinct or apical in Osniundacese, Ophiaglossaceae,, Marattiaceae, Salviniaceae, Marsiliaceae. PTERIDOPHYTA. 211 others each leaf has at its base an intrapetiolar, cap-like sheath, which protects the succeeding leaf. The leaves are of two kinds : (a) foliage, which in Ophioglossum vulgatum are lanceolate and entire, but in Botrychium however, are pinnate (6 in Fig. 208 J, J5); and (6) fertile, which are found facing the upper side of B 3. .4 Oi Jiioglossum vulgatufn, (Adder's-tongue) : Botrycliium lunaria (Moon- wort), both natural size ; r-n-oots; bs leaf-stalk ; ststem; l> foliage-leaf ; /fertile leaf. the foliage-leaves. These latter in Ophioglossum are undivided and spike-like (Fig. 209 A), but pinnate in Botrychium (Fig. 208 B). Each foliage and fertile leaf are branches from the same petiole. The large sporangia are placed laterally, and open by two valves. No annulus is formed (Fig. 209). Ophioglossum reproduces vege- tatively by adventitious buds on the roots. 212 PTERIDOPHYTA. Three genera with about twelve species. Order 2. Marattiacese are tropical Ferns, whose gigantic leaves resemble those of the Polypodiacese, but have stipules in addition. The sporangia are grouped in sori, situated on the lower side of the leaves, the sporangia in each sorus being arranged either in two rows or in a ring. In Angiopteris they are isolated (Fig. 210 A), but in the other species (Kaulfussia, Dancea, Marattia), they are united, and form "synangia" divided into a number of chambers corresponding to the sporangia. These open by clefts or pores. Marattia presents the highest development, as its sporangia are completely united in a capsule-like synangium, which is closed until maturity, and then opens by two valves. In each valve there is a row of three to eleven sporangia, each opening by a slit towards the inside (Fig. 210 B, C). An indusium encloses the sorus, except in Kanlfussia ; it is formed of flat and lobed hairs, which resemble the hairs of the other portions of the leaves. In An giopteris and Mar- attia the indusium is very rudimentary ; in Dancea it forms a kind of cupule. The numerous fossil Marattiaceae- (15 genera, with 98 species) present similar differences to those now living, but more various forms are found, for example, with solitary free sporangia. Those now living are the last small remnant (4 genera with only 2& species) of a once dominant family, which existed from very early times, FIG .210. Sporangia of the Marattiaceae : A Angiopteris; B and C Marattia; C is a half sorus with nine sporangia, each of which Las opened by a longitudinal cleft. and whose culminating point was reached in the Kulm and Coal periods. The Ophioglossaceas appear also in the Kulm and Coal periods, and were about as numerous as at the present time (presumably 2 genera, with 19 species). Leptosporangiate Ferns appear however to have occurred first of all in the Trias-formation. Family 2. Leptosporangiatse. Order 1. Polypodiaceae. Sporangia on the lower side of the leaves, talked and provided with a vertical, incomplete annulus \ dehiscing by a transverse cleft (Fig. 211 D). The genera are distinguished by the form of the indusium and the position of the sori, etc. PTER1POPHYTA. 213 1. The sporangia cover the entire lower surface of the leaf (Tropical America and Asia). Acrostichum, Platycerium. 2. Sori without indusia, circular or oval. Polypodium (Fig. 211 A}. The leaves are most frequently situated in two rows on the dorsal side of the creeping rhizome, and fall off leaving a smooth scar behind. P. vulgare, common in woods, on stones. (Phegu- pteris also has no iridusium ; see page 214). 3. The sporangia are situated in continuous lines just inside the margin of the leaf. Pteris 1 : the sporangia form a continuous line along the entire margin of the leaf (Fig. 211 C), which bends over and covers the sporangia, forming a " false-indusium." Pteridium has linear sori situated on a marginal vascular bundle, covered by two linear basal indusia, of which the outer is bent over like the edge of a leaf. P. aquilinum (Bracken; has a wide-spreading FIG. 211. Portions of leaves with sori. A Polypodium. B Aspidium. C Pteridium. I> A sporangium of one of the Polypodiaceae : r the annulus ; s spores. rhizome with large alternate leaves, placed on opposite sides, at some distance apart. Only one leaf is developed from each branch every year. Adiantum (Maiden-hair) : sori on the underside of small portions of the edge of the leaf, which are bent over (false indusium). Cryptogramme (Allosorus), Cheilanthes. 4. The sori are oval or linear, situated on one side of the vascular bundle. Asplenium (Fig. 212 J.) ; sori linear; indusium with one of its edges^ attached at the external side! A. ruta muraria (Wall-Rue) ; A. septentrionale ; A. trichomanes. Athyrium : sori linear cr curved; A. filix-fuemina (Lady-Fern). Scolopendrium 1 The former genus Pteris is divided into Pteris and Pteridium. 214 PTEEIDOPHYTA. (Fig. 212 B} : sori as in Asplenium, but situated in pairs across the lanceolate, entire leaves. Each sorus is covered on the ex- ternal side by an indusium, whose free edges are parallel and ap- proach each'othe'r. S. vidgare (Hart's-tongue). Blechnum (B. spicant, Hard Fern ; the fertile leaves differ from the barren, the pinnae being narrower, while the underside is almost entire'y covered with sori, and hence they are of a much darker brownish hue than the barren ones) Ceterach : indusium rudimentary or absent. 5. Sori circular and covered by a shield-like, or reniform indusium. Aspidium (Fig. 211 B) ; the leaves wither away and leave no scar upon the root-stock. A. filix-mas (Male-Fern) ; A. spinulosum. Phegopteris has no indusium, the withered bases of the leaf-stalks are persistent ; P. dryopteris and P. polypodioides. 6. The indusium is situated below the sori, and has the shape of a one-sided scale (Cystopteris, Struthiopteris}, or of a cup or cupule, which in Woodsia is sometimes fimbriate (Fig. 212 0, D). FIG. 212.^! Asplenium. B Scolopendrium. C Woodsia ; D single sorus of the same. E Cyathea : the sporangia have fallen off in the upper sori. (All magnified.) 7. The sori are situated on the margin of the leaf, and at the end of a vascular bundle. Indusium, semi-cupnlar. Davallia. Principally tropical species. 1 in S. Europe. This order is the greatest, comprising about 2,800 species, the A majority being perennial plants. few are large, and known as Tree-Ferns. As plants in conservatories and rooms the following are cultivated : species of Gymnogrartime (tropical America), Lomaria, Nephrolepis, Pteris (P. serrulata, cretica). Officinal. Aspidium filix -mas, rhizome and the withered petioles. Species of Alsophila and Cibotium give Penghawar Djambi. The rhizome of Pteridium aquilinum, var. esculentum, contains so much starch that it is used as food. The other orders of true Ferns deviate from the Polypodiacese, especially in PTERIDOPHYTA. 215 the formation of the ammlus, the bursting of the sporangium and its mode of attachment and development, and in the differences in the formation of the pro- thallium, etc. The principal are : Order 2. Hymenophyllaceae. To this order belong the lowest and most Moss-like Ferns ; the leaves, with the exception of the veins, are most frequently formed of only one layer of cells, and consequently stomata are wanting ; the formation of the prothallium also somewhat resembles the Mosses. Sori marginal, on the extremities of the vascular bundles, and surrounded by a cupular indiisium. The sporangia are sessile, with equatorial annulus. Hy- menopliyUum (H. tunbridgense, European). Trichomanes (T. speciosum, Euro- pean). Species about 200, which live especially on rocks and trees in damp and shady tropical forests. Some have no roots. Order 3. Cyatheaceae. Annulus complete and oblique. To this order be- long, principally, the tree-like Ferns with palm-like habit. The number of ppecies is about 200, .they are all tropical and form forests in some regions of Australia. Cibotium and Dicksonia have marginal sori, with cupular, basal indusium. (The stem of D. antarctica is covered with aerial roots.) Alsophila (without indusium) ; Cyathea with cupular, inferior indusium (Fig. 212 E). FIG. 213. Gleiclienia : A part of a leaf with sori ; B a single sorus. Order 4. Gleicheniaceae. Sporangia with equatorial annulus, and longitudinal dehiscence, most frequently groups of 3-4 in sori without indusium (Fig. 213). Gleiclienia: the apical growth of the leaves continues for a long time. Order 5. Schizaeaceae. Annulus apical. To this order belongs Aneimia, which is so commonly cultivated in conservatories. The two lowest pinnae are metamorphosed, having no leaf-parenchyma and being covered with sporangia. Schizcea. Mohria. Lygodium, a climber, whose leaves have unlimited growth and attain a length of several metres. About 70 species. Tropical. Order 6. Osmundaceae. The sporangia have at the apex a lateral group of strongly thickened cells, which gradually pass over into the ordinary cells. The sporangia open by a longitudinal cleft. Indusium wanting. Osmunda bears the sporangia upon peculiar, branched pinnae, without parenchyma (the uppermost in the leaf). 0. regalis (Royal-Fern) : European. Sub-Class 2. Hydropterideee (formerly Rhizocarpae), Water Ferns. The following further characteristics must be added to those given on page 205 : 216 PTERIDOPHYTA. Sexual generation. The MICROSPORES produce an extremely rudimentary prothallium, formed of only two cells, and having D FIG. 214. Sulrinta natans : A miorosporanginm with germinating microspores and pro- trading prothallia (s) ; B a prothallium with the bicellular antheridium (s) growing out of the microsporangium ; C the two cells of the antheridium have opened by transverse clefts ;