216 



PTERIDOPHYTA. 



Sexual generation. The MICROSPORES produce an extremely 

 rudimentary prothallium, formed of only two cells, and having 



D 



FIG. 214. Sulrinta natans : A miorosporanginm with germinating microspores and pro- 

 trading prothallia (s) ; B a prothallium with the bicellular antheridium (s) growing out of 

 the microsporangium ; C the two cells of the antheridium have opened by transverse 

 clefts ; beneath is seen the microspores enclosed by the hardened mucilage ; D spermato- 

 zoids still enclosed in the mother-cells. 



also a very much reduced bicellular antheridium with a small 

 number of spermatozoid mother-cells in each cell (in Salvinia 4, in 

 Marsilia and Pilularia 16). In Salvinia the microspores remain 

 embedded in a hard mucilaginous mass (at first frothy) which fills 

 up the cavity of the sporangium. The prothallinm must therefore 



FIG. 215. Sahinia natans. A, B Female prothnllin,/-/, protruding from the macrospore 

 which is still enclosed in the macrosporangium; ce archegonia. C An embryo (x 16) 

 still in connection with the spore (s) : a the scutiform leaf ; b-e the subsequent foliage- 

 leaves, of which b and c stand singly, d-e-v in a whorl ; v the submerged-leaf ; /-/ wing, 

 like lobes of the prothallium ; m the foot. 



