288 



MORPHOLOGY. 



upper end. Here the nucleus divides a great many times, and 

 finally cell walls are formed, so that a tissue of considerable ex- 

 tent is formed inside the wall of the spore, which is very 

 different from what takes place in the ferns we have 

 studied. As the prothallium matures the spore is cracked 

 at the point where the three angles meet, as shown in 

 fig- 334- The archegonia are developed in this exposed 

 surface, and several can be seen in the illustration. 



588. Embyro. After fertilization the egg divides in such a way 

 that a long cell called a suspensor is cut off from the upper side, 



Fig- 333- 



Section of mature macrospore 

 of selagmella, showing female 

 prothallium and archegonia. 

 After Pfeffer. 



. 334- 



Mature female prothallium of 

 selaginella, just bursting open 

 the wall of macrospore, exposing 

 archegonia. After Pfeffer. 



Fig. 335. 



Seedling of sela- 

 ginella still attached 

 to the macrospore. 

 After Campbell. 



which elongates and pushes the developing embyro down into the center of 

 the spore, or what is now the female prothallium. Here it derives nourish- 

 ment from the tissues of the prothallium, and eventually the root and stem 

 emerge, while a process called the " foot " is still attached to the prothallium. 

 When the root takes hold on the soil the embyro becomes free. 



