CH. X] 



PROTHALLUS. 



133 



stages the young oophyte is differentiated into a green 

 aerial or assimilating part and terrestrial root-like part. 

 The green part now grows and by a series of cell divisions 



FIG. 59. 



DEVELOPMENT OP PROTHALLUS FROM THE SPORE. 



a, germinating spore ; s, the cell wall of the spore ; the new growth has 

 already divided into r.h., a root-hair and p t which contains chloro- 

 plasts and by further division forms the prothallus. 

 6, c, d t older stages, c and d, less highly magnified, 

 a and &, Dicksonia antarctica, c and d, Aspidium filix mas. 

 (After Luerssen.) 



forms a flat, heart-shaped body, which is known as a pro- 

 ihallus. The central part of the prothallus is thickened 

 into a cushion-like ridge several cells in thickness, the 

 rest of the expanse consists of a single layer of cells. It 

 grows with the cushioned side downwards attached to the 

 soil by numerous root-hairs and is now a full-grown 

 oophyte leading an independent life, and as above pointed 

 out, of a form extremely distinct from that of the 

 sporophyte which gave it birth. 



