262 



BRYOPHYTA 



habit, surrounded as it is up to full maturity by the tissues of the parent 

 thallus. But the larger sporogonia of the Marchantiaceae project at 

 maturity from their envelopes, and even during development their relation 

 to the parent thallus is not uniform all round, their nutrition emanating 

 mainly from base of the archegonium : a certain degree of polarity, 

 expressed in the formation of a sterile foot for nutritive and mechanical 

 purposes, is thus intelligible. 





FIG. 122 



Monoclca Forsteri, Hook. 47 = part of a longitudinal section of a capsule showing 

 elaters and rows of spore-mother-cells. X350. 48 = longitudinal section of the tip of a 

 nearly mature capsule, showing the lobed spore-mother-cells. X 160. 49 = elaters, tetrads 

 of spores, and a cell from the wall of a still more mature capsule. X35o. (After Johnson.) 



But much more interest attaches to the internal differentiation of the 

 capsule. The wall is initiated at a relatively early stage, and remains a 

 single layer, excepting at the extreme apex : the mass of tissue which lies 

 within, corresponding as it does in position to the sporogenous cells of 

 Riccia, is composed of cells all alike in origin, and it is often designated 

 the archesporium (Fig. 121 iv.). But they do not all develop as .spore- 

 mother-cells : some become elongated, and form the well-known sterile 

 elaters (Fig. 121 v. el) ; others, undergoing more numerous divisions, 

 remain fertile, and divide into spore-tetrads : a later stage of this differ- 

 entiation is well illustrated in Fig. 122 for Monoclea, a genus of doubtful 



