350 



MOSSES AND FERNS 



CHAP. 



The prothallia of the Osmundacege often form adventitious 

 buds, much Hke those of the Marattiacese. These secondary 

 prothalha (Fig. 194, B) generally arise from the margin, but 

 may be produced from the ventral surface. An apical cell is 

 usually early established, and the subsequent growth is closely 

 like that of the primarv one. 



A. 



Fig. 193. — A, Apex of a young prothallium of O. Claytoniana, with two similar initials, 

 X, X, Xs6o; B, longitudinal section of an advanced prothallium of O. cinnamomea, 

 X260; C, horizontal section of a similar one, showing two initials, X260. 



The prothallia are long lived if they remain unfertilised, 

 and Goebel ((i6), p. 199) states that in O. regalis they may 

 reach a length of four centimetres. He also records a genuine 

 dichotomy of the older prothallia of this species. 



The Aiithcridmm 



Under favourable circumstances the first antheridia appear 

 after about a month in 0. Claytoniana, and continue to form 



