210 



MOSSES AND FERNS 



CHAP. 



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

 of the columella remains. 



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

 Ephoiierum in the development of the sporophyte. 



The highest members of the Cleistocarpae, such as Phasciim 

 and rieiiridiiDu (Fig. 116), approach very closely in structure 

 the stegocarpous Bryales. In these the gametophore is much 

 better developed than in Ephcmcriun, and the protonema not 

 so conspicuous. The leaves also frequently have a well- 

 developed midrib which is wanting in the leaves of Ephcmeriim. 

 Kienitz-Gerlofif (2) has carefully studied the embryogeny 

 of Phascwn cuspidatnm, and except in a few minor details it 



corresponds verv closely to that of 

 Fnnaria, except, of course, as re- 

 gards the operculum and peristome, 

 which are absent. In Phascum, 

 however, the archesporium is dif- 

 ferentiated earlier than in Fnnaria. 

 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 tlie columella 

 (Fig. 115, D). The outer spore- 

 sac has but two lavers of cells, and 

 the capsule wall three, and between 

 them the large lacuna is formed as 

 in Fnnaria; but in Phascum as in 

 Ephcmcrnm, the separation of the 

 cells is complete. In the seta a 

 slightly-developed central cylinder of conducting tissue is de- 

 veloped, derived, as in Fnnaria, from the endothecium, but in 

 Phascnm it is much less conspicuous. Plenridinm (Fig. 

 115, A) in its later stages corresponds exactly to Phascnm, 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. — PleuriJium 

 X20. 



subulatum. 



