BRYALES 



283 



Phascum : the sterilisation of the whole of the upper products of the 

 endothecium at the narrow distal end of the fertile tract would interrupt 

 the dome, and complete the columella, just as it is seen in Phascum. 

 There is no inherent im- 

 probability in this, but 

 rather the reverse : for it 

 would be only introducing 

 one further step in sterili- 

 sation. On such grounds 

 the relation of the Phasca- 

 ceae to the Andreaeaceae 

 would appear to be a near 

 one. 



Another simple Cleisto- 

 carpic form which has not 

 only been observed exter- 

 nally, but also worked out 

 developmentally, is Nano 

 mitrium tenerum. The 

 small capsule has here a 

 provision for dehiscence 

 by the formation of a 

 rudimentary annulus. The 

 segmentation of the embryo 

 begins on the plan of the 

 Bryales (Fig. 140, i.), and 

 there is as usual a differen- 



r , j ..u through a sporogonium after formation of the air-space ; s/ = arche- 



tiatlOn OI the endOtneClUm sporium; .y/.r = spore-sac; = limits between amphithecium and 



j uvu ' /T?' endothecium. J3 = transverse section of the same. (After Kienitz- 



and amphithecium (rig. Gerioff.) 



140, ii.). The cells of the 



latter, after further division, become differentiated into an exiguous central 



columella, surrounded by relatively numerous and somewhat irregularly 



arranged spore-mother-cells (Fig. 140, iv.) : but as maturity approaches the 



columella disappears, its materials having served for nourishing the spores 



which fill the cavity of the capsule. 



The genus Ephemerum is closely related with that of Nanomitrium, 

 from which it differs in the absence of any definite operculum : the 

 condition of the columella is the same, but while it disappears at 

 maturity in some species (E. papillosum\ in others it may still be seen 

 in the mature capsule (E. crassineruiutri). The fact that stomata occur 

 on the capsule-wall, though when ripe this is only a single layer in 

 thickness, has its bearing on the question whether these simple Mosses 

 are primitive or reduced forms. A systematic position is now assigned 

 to them by many writers apart from other Cleistocarpic forms, in close 

 relation to the Funariaceae. 



FIG. 139. 

 Phascum cuspidatum, Schreb. Schut. A longitudinal section 



