. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 2l6 MOSSES AND FERNS CHAP. whole of the capsule is filled with the large spores, and no trace of the columella remains. Nanomitrium (Goebel (22), p. 374), closely resembles Ephemerum in the development of the sporophyte. The highest members of the Cleistocarpse, such as Phascum and Fleuridium (Fig. 116), approach very closely in structure the stegocarpous Bryales. In these the gametophore is much better developed than in Ephemerum, and the protonema not so conspicuous. The leaves also frequent
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 2l6 MOSSES AND FERNS CHAP. whole of the capsule is filled with the large spores, and no trace of the columella remains. Nanomitrium (Goebel (22), p. 374), closely resembles Ephemerum in the development of the sporophyte. The highest members of the Cleistocarpse, such as Phascum and Fleuridium (Fig. 116), approach very closely in structure the stegocarpous Bryales. In these the gametophore is much better developed than in Ephemerum, and the protonema not so conspicuous. The leaves also frequently have a well- developed midrib which is wanting in the leaves of Ephemerum. Kienitz-Gerlofif (2) has carefully studied the embryogeny of Phascum cuspidatum, and except in a few minor details it corresponds verv closely to that of Funaria, except, of course, as re- gards the operculum and peristome, which are absent. In Phascum, however, the archesporium is dif- ferentiated earlier than in Funaria. In each of the four primary cells of the endothecium, as seen in trans- verse section, a periclinal wall arises which at once separates the archesporium from the columella (Fig. 115, D). The outer spore- sac has but two layers of cells, and the capsule wall three, and between them the large lacuna is formed as in Funaria; but in Phascum as in Ephemerum, the separation of the cells is complete. In the seta a slightly-developed central cylinder of conducting tissue is de- veloped, derived, as in Funaria, from the endothecium, but in Phascum it is much less conspicuous. Fleuridium (Fig. 115, A) in its later stages corresponds exactly to Phascum, ex- cept that the capsule is more slender. In both of these genera the seta remains short, but is perfectly evident. Whether the absence of a distinct operculum in the cleistocarpous Mosses is a primitive condition, or whether they are reduced forms, it is impossible to determine positively from a study of their em- Fig. h6.—Pleuri
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