2l6 



MOSSES AND FERNS 



CHAP. 



whole of the capsule is filled with the large spores, and no trace 

 of the columella remains. 



Nanomitnum (Goebel (22), p. 374), closely resembles 

 Ephemerum in the development of the sporophyte. 



The highest members of the Cleistocarpae, such as Phascum 

 and Pleuridium (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 Ephemermn. 

 Kienitz-Gerloff (2) has carefully studied the embryogeny 

 of Phascum cuspidatuin, 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 tw r o 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. Pleuridium (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- 

 bryogeny. 



FIG. 116. Pleuridium 



X20. 



subulatum, 



