Foreshortening

“ No better idea of their size can be gleaned than to record the fact that in each sorus there may be about one hundred small, often short-stalked spore cases, known as sporangia, and that in each sporangium well over forty, and sometimes over sixty, spores will be crowded. A healthy specimen of many of our common ferns will bear about ten or a dozen leaves, each of which is divided into many divisions, and among these divisions of the leaf there may be at least fifty that bear from fifteen to twenty sori. ”

“ Fig. 257.—Sori and Sporangium of Polypode. A chain of cells lies along the top of the sporangium, which springs back elastically on drying, thus disseminating the spores. Fig. 258.—The Brake Fruits underneath the Revolute Edges of the Leaf. Fig. 259.—Fruiting Pinnules of Maidenhair Fern.
The sporangia are collected into little groups, known as sori (singular, sorus) or fruit-dots. Each sorus is covered with a thin scale or shield, known as an indusium. This indusium separates from the frond at its edges, and the sporangia are exposed. Not all ferns have indusia. ”

“ Spores developing into flat or irregular prothallia, which bear the reproductive organs (antheridia and archegonia) ; flowers and seeds none. 1. Spores produced in sporanges, which are borne on the back of a leaf, in spikes or panicles, or in special conceptacles. Order 1. Filicales. Spores all of one sort and size (isosporous families) . Vernation erect or inclined; sporanges in spikes, or panicles, opening by a transverse slit. Fam. 1. Ophioglossaceae. Vernation coiled; sporanges reticulated, usually provided with a ring (annulus) . ”

“ When the prothallus of a fern has developed normally, it is a flattened leaf-like structure which bears rootlets and male and female genital organs on the lower surface, i.e., on that turned from the light. But the experimenter may reverse this [Pg 50] order, by artificially shading the upper surface, and strongly illuminating the lower surface.
Among the most interesting heteromorphoses are the galls, produced upon young plants when certain insects lay eggs on them, or when plant-lice irritate their tissues. ”

“ C the two cells of the antheridium have opened by transverse clefts; beneath is seen the microspores enclosed by the hardened mucilage; D spermatozoids still enclosed in the mother-cells.
Fig. 215.—Salvinia natans. A, B Female prothallia, f-f, protruding from the macrospore which is still enclosed in the macrosporangium; œ archegonia. C An embryo (× 16) still in connection with the spore (s) : a the scutiform leaf; b-e the subsequent foliage-leaves, of which b and c stand singly, d-e-v in a whorl; v the submerged-leaf; f-f wing-like lobes of the prothallium: m the foot.
Sexual generation. ”

“ The united edges of a carpel which bear the ovules are termed the ventral suture. The back of the carpel forms the dorsal suture. The Marsiliaceæ take a position among the Hydropterideæ analogous to that occupied by the Angiosperms; the sporangia are in a corresponding manner enveloped in a closed leaf.
The collection of stamens in a flower is termed the andrœcium, and all the carpels, whether individually free or united into one pistil, the gynœceum.
The Sporangia. The asexual generation of the Mosses is the sporogonium, in which the spores arise in tetrads from the mother-cells. ”

“ Sporangia scattered, orange or nut-brown, very minute, .1–.3 mm. or less, globose or ellipsoidal, stipitate, erect or nodding; hypothallus none; stipe short, 1–3 times the sporangium, filiform, tapering upward, brown; the calyculus variable, sometimes well marked and separated from the net when fully mature, by a shallow constriction, more commonly small or entirely wanting, especially in the spherical sporangia; net simple, large meshed, without nodal expansions, the threads flattened; spore-mass yellow, spores by transmitted light, pale, nearly smooth, 5–6 μ.
A most beautiful tiny species. ”

“ In several species the stem stele is endarch. Our knowledge of the leaves is very meagre: in B. forensis they were repeatedly branched and apparently bore small fleshy pinnules; the sporangia, though differing from those of recent ferns, may be compared with the spore-capsules of Osmundaceae as regards the structure of the annulus. The abundance of hairs on the stems and leaves of some species, the tracheal sheath in the sporangium described by Oliver [1131] as Tracheotheca (= Botryopteris?) ”

“ The spore on germination gives rise to a small thalloid structure, the prothallium, on which the sexual organs are developed; this is the gametophyte or sexual generation. The sexual organs have the form of typical archegonia and antheridia. From the fertilised egg-cell there is developed the Pteridophyte plant or sporophyte, which bears the spores. This asexual generation shows a well-marked external differentiation into stem and leaves, and bears true roots. Internally the tissues exhibit a high degree of differentiation into distinct tissue-systems. ”

“ The sporangia bear spores of one kind only; the wall of a sporangium consists of one layer of cells. In the great majority of cases the sporangia are characterised by the possession of a conspicuous row of thick-walled brown cells, the annulus [683] , which serves as a mechanism for dehiscence and spore-dispersal. The fertile leaves, identical in form with 284the sterile, or more or less sharply contrasted, usually bear the sporangia on the under surface of the lamina in definite groups or sori, and not on the upper surface or grouped in strobili as in the Lycopodiales. ”

“ Plants more or less fern-like consisting of a stem with a single leaf. In Ophioglóssum the leaf or sterile segment is entire, the veins reticulated and the sporangia in a simple spike. In Botrýchium the sterile segment is more or less incised, the veins free, and the sori in a panicle or compound or rarely simple spike. Sporangia naked, opening by a transverse slit. Spores copious, sulphur-yellow. ”

“ In the fresh-water algæ the two more general methods of multiplication are clearly governed by the conditions of the seasons; the resting-spores securing continuity of life during the winter, the swarm-spores spreading the plant profusely during the warmer portion of the year, when rapid growth is possible. I therefore regard the actively swarming bodies seen in continuous motion at the two extreme portions of the frustule of Closterium lunula as being either oospores or zoospores, by means of which reproduction takes place. ”

“ Sporangia collected in dots, lines, or variously shaped clusters (sori or fruit-dots) on the back or margins of the frond or its divisions, cellular-reticulated, stalked, the stalk running into a vertical incomplete many-jointed ring, which by straightening at maturity ruptures the sporangium transversely on the inner side, discharging the spores. Fruit dots often covered (at least when young) by a membrane called the indusium (or less properly the involucre) , growing either from the back or the margin of the frond. ”

“ In what may be regarded as the type of normal life-history, the transition from the one generation to the other is marked by definite processes: there is the meiotic development of spores by the sporophyte, and the sexual production of a zygote, or something analogous to it, by the gametophyte. But it has been mentioned in the preceding pages that the transition may, in certain cases, be effected in other ways, which may be regarded as abnormal, though they are constant enough in the plants in which they occur, in fact as manifestations of reproductive degeneration. ”

“ A mycelium which has sprung from one spore, whose position is marked by the *: a, b, c are three sporangia in different stages of development; a is the youngest one, as yet only a short, thick, erect branch; b is commencing to form a sporangium which is larger in c, but not yet separated from its stalk.
[98]
The Mucoraceæ, in addition to the chlamydospores and oidia, have a more normal and ordinary method of reproduction; viz., by spores which are formed without any sexual act. Mucor has round sporangia ”

“ Rejuvenescence gives rise to a swarm-spore or zoospore. The whole of the protoplasm of a cell contracts, becomes rounded and rearranged, and escapes into the water, in which the plant floats as a mass of protoplasm, clear at one end and provided with cilia by which it is enabled to move, until after a time it comes to rest, and after secreting a wall forms a new plant by ordinary cell-division. Example: Oedogonium.
2. Free-cell formation forms swarm-spores which behave as above. ”

“ The foraminifer multiplies by fission, or by a process of budding. In some species the division of the protoplasm is complete, as in the case of amœbæ, so that each animal has its own shell which encloses a single chamber, but in most cases the ‘bud’ remains attached to a parent cell, and develops a shell that is also fixed to the shell of its progenitor. The younger animal thus produced from the bud gives rise to another, which develops in the same manner ”

“ Some are capable of moving from cell to cell in the body as do the white blood-corpuscles. They all agree in the production of spores—hence the name.
At certain stages in their development the nucleus within the body of the organism divides again and again until there are a great many daughter nuclei, each accompanied by a small mass of protoplasm, often inclosed in a little sac or cyst of its own. This is the process of spore-formation and we see that from a single individual we may have by division, not two animals as in the amœba, but a score or more of them. ”

“ Sporogony.—This method of reproduction has been described by E. Metchnikoff in Cunina and allied genera. In individuals either of the male or female sex, germ-cells which are quite undifferentiated and neutral in character, become amoeboid, and wander into the endoderm. They divide each into two sister-cells, one of which—the spore—becomes enveloped by the other. The spore-cell multiplies by division, while the enveloping cell is nutrient and protective. The spore cell gives rise to a “spore-larva,” which is set free in the coelenteron and grows into a medusa. ”

“ Nevertheless, it often happens that all the glands do not become completely dry; and in this case delicate objects, such as fragile insects, are sometimes torn by the re-expansion of the tentacles into fragments, which remain scattered all over the leaf. After the re-expansion is complete, the glands quickly begin to re-secrete, and as soon as full-sized drops are formed, the tentacles are ready to clasp a new object. ”

“ The sexual generation is represented by a small green prothallus which lives for a short period only and dies after nursing the fern-plant through its earliest stages.
(b) Hydropterideae. Heterosporous water-ferns differing considerably in habit from the true ferns. Each megasporangium contains a single megaspore and several microspores are produced in each microsporangium. The gametophyte is represented by tissue more or less enclosed in the spore. [Genera Salvinia, Azolla, Marsilia, Regnellidium, Pilularia. See Chapter XXVI.]
Eufilicineae. ”

“ Sporanges opening vertically. Sporanges panicled, with a rudimentary ring; marsh ferns. Fam. 2. Osmundaceae. Sporanges sessile on a filiform receptacle; leaves filmy, translucent. Fam. 3. Hymenophyllaceae. Sporanges ovoid, in panicles, or spikes, provided with an apical ring. Fam. 4. Schizaeaceae. Sporanges opening transversely, provided with a vertical ring; borne in sori on the back or margin of a leaf. Fam. 5. Polypodiaceae. Spores of two sizes (microspores and macrospores) . Plants rooting in the mud; leaves 4-foliolate, or filiform. Fam.6. Marsileaceae. Plants floating ”

“ Although it is impossible without the evidence of development to decide with certainty between these alternatives, it would seem most probable that a sporangiophore may be looked upon as a ventral lobe of a leaf, the sterile lobes forming the bracts or members of the sterile whorls of the cone. This question is discussed by Zeiller [887] and Williamson and Scott [888] , also more recently by Scott [889] in his memoir on Cheirostrobus.
Sphenophyllostachys Römeri (Solms-Laubach) [890] . Fig. ”

“ Internal parasites and "saprophytes," that is, beings which live on dead and decayed organic matter, on the other hand, live surrounded by a supply of dissolved food; and rarely do we find larger cells, richer in reserves, than in the parasitic Sporozoa, which owe their name to the importance of brood-formation in their life-history. In Radiolaria (p. 75 f.) a central capsule separates off an inner layer of protoplasm; the outer layer is the one in which digestion is performed, while the inner layer stores up reserves; and here brood-formation appears to be the rule. ”

“ The sporangia, which are situated singly on the adaxial surface of the leaves, between their insertion on the stem and the ligule, arise from a considerable number of epidermal cells. The cells composing the young sporangium are at first similar, but ultimately become differentiated into sterile trabeculae, which may stretch from the inner to the outer wall, and the mother-cells of the spores. The latter are more numerous in the microsporangium than in the megasporangium. The tapetal layer is partly formed from the sporangial wall and partly as a layer covering the trabeculae. ”

“ The spore-bearing generation may throughout its phylogenetic history have been independent at one part of its life, and have been derived by modification of individuals homologous with those of the sexual generation, and not by the progressive sterilization of a structure the whole of which was originally devoted to asexual reproduction. ”