. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 402 MOSSES AND FERNS CHAP. Up to this point the exospore remains intact; the central cell of the archegonium is only separated from the spore cavity by a single layer of cells, and the young prothallium agrees closely with Prantl's account of the similar stage of Salvinia (Fig. 235, A, B). Berggren's figures of A. Caroliniana, at a stage presumably the same, are too diagrammatic to allow of a satisfactory comparison. Shortly after the first division in the archegonium a rapid increase takes pl
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 402 MOSSES AND FERNS CHAP. Up to this point the exospore remains intact; the central cell of the archegonium is only separated from the spore cavity by a single layer of cells, and the young prothallium agrees closely with Prantl's account of the similar stage of Salvinia (Fig. 235, A, B). Berggren's figures of A. Caroliniana, at a stage presumably the same, are too diagrammatic to allow of a satisfactory comparison. Shortly after the first division in the archegonium a rapid increase takes place in the size of all the cells of the prothal- lium, by which it expands and ruptures the exospore, which breaks open by three lobes at the Fig. 235.—Azolla iiliculoides. A, Longitudinal section through the upper part of the germinating macrospore, X220; b, b, the basal wall of the prothallium; ar, young archegonium; «, free nuclei; B, similar section of a nearly developed female pro- thallium, X220; C, D, archegonia, X375', K neck canal cell; v^ ventral canal cell; o, egg; E, two transverse sections of a prothallium with the three first archegonia, X160; F, median section of a macrospore with large prothallium ipr), X65; t»» indusium; sp^ remains of sporangium wall; ep, perinium. The most remarkable difference between Azolla and the other Hydropterides is the further development of the lower of the two primary nuclei.^ In Azolla it undergoes repeated divisions, and the resulting nuclei remain embedded in the protoplasm in close proximity to the lower cells of the pro- ' Recently Coker (i) has observed a fragmentation of the nucleus in Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Campbell, Douglas Houghton, 1859-1953. New York, The Macmillan Company;
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