XI THE HOMOSPOROUS LEPTOSPORANGIAT.'E 341 



the four quadrant cells are formed, one of the terminal ones 

 becomes at once the apical cell. 



As soon as the apical cell is established, growth proceeds 

 as in Onoclea, and a heart-shaped prothallium is formed. One 

 difference, however, may be noted. Each segment cut off from 

 the apical cell divides first by a transverse wall into an inner 

 and an outer cell, but the inner cell from the first undergoes 

 divisions by horizontal walls, so that a central midrib is formed, 

 very much as in Metzgeria, and the prothallium becomes more 

 elongated than is common in the Polypodiaceae. The single 

 two-sided apical cell persists for a long time, but is finally 

 replaced either by a single cell, much like that of Pellia 

 epiphylla, or more commonly by a series of marginal cells, as 

 in the Marattiacea; or Polypodiaceae. The subsequent growth 

 of the prothallium is the same as in those forms, but no 

 definite relation could be made out between the archegonia 

 and the segments of the initial cells. Among the Hepaticse 

 Dendroceros offers almost an exact analogy in the form of 

 the apical cells and the divisions of the segments. 



According to Luerssen,^ in Todea a distinct apical cell is 

 often wanting, and the growth throughout is due to the activity 

 of several similar initials. His figures, however, hardly bear 

 out his statement, and further information is desirable on this 

 point. 



As the prothallia grow older the midrib becomes conspicu- 

 ous, and projects strongly from the ventral surface. In O. 

 cinnainomea and O. regalis even at maturity it is very little 

 broader where the archegonia are formed, but in 0. Claytoniana 

 it forms a cushion in front, much like that of Marattia or the 

 Polypodiaceae, and in this respect, as well as the form of the 

 apical cells, seems to approach the latter. In this species the 

 prothallium is lighter coloured, and the root-hairs not so dark, 

 while in its dark green colour and fleshy texture 0. cinnainomea 

 recalls AntJioceros IcEvis or Marattia. 



Where a cell mass is formed at first, this condition is 

 temporary, and an apical cell is established which gives rise to 

 the ordinary flat prothallium. The small male prothallia, which 

 are formed in large numbers, exhibit various irregularities, and 

 quite commonly do not show any definite apical growth, and in 

 O. Claytoniana especially often branch irregularly, or in some 



^ Luerssen (3). 



