PTEEIDOPHYTA— HyDEOPTEEIDE.E 



149 



Fig. 907. 



The lower cell takes no part in the formation of the 

 prothallium, but remains ahnost unchanged, becoming filled with 

 various reserve materials for 

 the nutrition of the young 

 embryo developed later on the 

 prothallium. In Azolla its 

 nucleus divides repeatedly, 

 but no cell- walls are formed 

 in it. 



The archegonia are de- 

 veloped at the apex of the 

 prothallium, three being 

 usually formed in Salvinia, 

 but only one in the Mar- 

 sileaceae and Azolla. If none 

 of the first formed ones be- 

 come fertilised, more are de- 

 veloped later. The structiu-e 

 is similar to that of the ferns. 



In the germination of the 

 zygote or oospore Salvinia 

 shows some peculiar features. 

 It segments into octants as 

 in the Ferns, but all the 

 hypobasal cells go to form 



the foot. No root is developed, ng. 907. Gametopliyte produced by the 

 The first leaf or cotyledon, macrospore of Salmnia. pro Prothallium 



, bearing a, young sporophyte. After 



developed from two of the Priugsheim. 



epibasal cells, is of curious 



shape. It is known as the scutiform leaf. In the other three 



genera there are two cotyledons, stem, and root, as well as foot. 



