Sporangium

“ 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. ”

“ Sporangia simple and stipitate or sessile, sometimes plasmodiocarp, rarely combined into an aethalium; the wall a thin membrane, usually with an outer layer of minute roundish granules of lime. Stipe present or often wanting, seldom prolonged within the sporangium as a columella. Capillitium consisting of slender tubules, which branch repeatedly in every direction and anastomose to form an intricate network, the extremities attached on all sides to the wall of the sporangium ”

“ In S. grandis (figs. 130, 3; 131, G) the long and narrow strobili consist of a slender axis bearing imbricate sporophylls in four rows: each sporophyll subtends a sporangium situated between the ligule and the axis of the shoot. The sporangium may be developed from the axis of the cone or, as in Lycopodium, from the cells of the sporophyll [126] . In some species the lower sporophylls bear only megasporangia, each normally containing four megaspores, the microsporangia being confined to the upper part of the cone. ”

“ Stipe short, erect, rugulose, brown or blackish, expanding at the base into a small hypothallus; the columella reduced to a thin layer of minute brown scales upon the base of the sporangium. Capillitium of simple or sparingly-branched threads, colorless at the extremities and dark-colored between. Spores globose, even, violaceous, 6–8 mic. in diameter.
Growing on old leaves, sticks, herbaceous stems, etc. The sporangium .6-.8 mm. in diameter, the stipe about the same length. Fries considered this to be a mere variety of D. farinaceum, but it is readily distinguished by its very small spores. ”

“ Sporangia tufted, generally in medium-sized clusters much as in S. fusca. The individual sporangium 7–9 mm. high, dark, slender, brown, becoming dull black or pallid as the spores are lost, stipitate, the stipe about one-fourth to one-third the total height, black polished shining; hypothallus distinct, common to all sporangia, purple-brown, shining; columella distinct, attaining almost the summit of the sporangium but inclined to waver a little at last, in other words, flexuose toward the top, freely branching, the branches rather stout, anastomosing to support the capillitial net ”

“ When the ripe sporangium becomes dry, the ring of thickened cells (an.) contracts more strongly than the others, and acts like a spring pulling the sporangium open and shaking out the spores, which germinate readily under favorable conditions, and form after a time the sexual plants (prothallia) .
The roots of the sporophyte arise in large numbers, the youngest being always nearest the growing point of the stem or larger roots (Fig. 67, C) . The growing roots are pointed at the end which is also light-colored, the older parts becoming dark brown. ”

“ Sporangia gregarious, large, 1 mm. in diameter, dark purple, erect, stipitate, depressed-globose; stipe concolorous, furrowed, about twice the diameter of the sporangium in length, with a distinct hypothallus; calyculus persistent, less than half the sporangium, obscurely ribbed, marked by concentric plications, the margin toothed; the net poorly differentiated, the meshes irregular in form and size, as are also the flat, unthickened nodes, the threads pale, free ends short and not numerous; spore-mass purple; spores by transmitted light, pale or colorless, 5–6 μ, smooth. ”

“ 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. ”

“ In the absence of the female reproductive organs, the seeds, we cannot in most cases be certain whether the small sporangium-like bodies on fertile pinnules are true fern sporangia or the microsporangia of a heterosporous pteridosperm. What is usually called an exannulate fern sporangium, such as we have in Angiopteris and in many Palaeozoic plants, has no distinguishing features which can be used as a decisive test. The microsporophylls of the Mesozoic Bennettitales produced their spores in sporangial compartments grouped in synangia like those of recent Marattiaceae ”

“ A spore-wall is soon secreted and the sporangium has now resolved itself into a mass of spores, traversed by the strands of the capillitium and enclosed in a sporangium-wall, connected with the substratum by a stalk. As ripening proceeds, the wall becomes membranous and readily ruptures, and the dry spores may be carried abroad on the currents of air or washed out by rain. ”

“ In the formation of sporangia two cells fuse together by means of outgrowths, in a manner very similar to that of Spirogyra; sometimes, however, the wall between two cells merely breaks down. The fused cell becomes a sporangium, and in it eight spores are developed. In certain cases single cells develop parthenogenetically, without fusion, each cell producing, however, only four spores. ”

“ 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. ”

“ In the region of the cone the internodes remain shorter, and the whorls of appendages, known as sporophylls or sporangiophores, have the form of stalked structures terminating distally in a hexagonal peltate disc, which bears on its inner face a ring of five to ten oval sporangia (fig. 52, B) . Each sporangium contains numerous spores which249 eventually escape by the longitudinal dehiscence of the sporangial wall. The opening of the sporangia is probably assisted by the movements of the characteristic elaters formed from the outer wall of each spore. ”

“ The sporangia are borne singly or in sori of two or three on the margin or under surface of leaves, the fertile pinnae of which differ more or less from the sterile segments. The sporangium is of considerable size, and dehisces by a median slit, the annulus being a more or less definitely limited horizontal ring of cells near the apex. The prothallus and sexual organs may resemble those of the Polypodiaceae; in Aneimia and Mohria the prothallus, though flattened, is not bilaterally symmetrical, the growing point being on one side; a filamentous type of prothallus is known in Schizaea. ”

“ The peridium may be double, varies in texture, color, persistence, and so forth, as will be more fully set forth in the several specific descriptions. The peridium blends with the hypothallus below when such structure is recognizable, either directly, when the sporangium is sessile, or by the intervention of a stipe. The stipe may be hollow, may contain coloring matter of some sort, or may even contain peculiar spore-like cells or spores; is often furrowed, and in some cases shows a disposition to unite or blend with the stalks of neighboring sporangia. ”

“ Sporangia crowded, generally in dense colonies, globose, smooth, ochraceous-white, stipitate, the peridium thick, cartilaginous, splitting from above into several petal-like lobes, which become speedily reflexed exposing the swarthy spore-mass, the inner peridium not discoverable, inseparable; stipe concolorous, about equal to the sporangium; hypothallus, generally well developed, but thin, membranaceous, common to all the sporangia; columella prominent, globose or cylindric, often constricted below, and prolonged upward almost to the top of the spore-case ”