The Ferns and Their Allies 



289 



When mature, the pro- 

 thallus produces egg cells 

 and sperms m small organs 

 on Its under surface. The 

 sperms are small and swim 

 actively, and they reach the 

 egg cells when the thallus 

 is wet. The sperm tinites 

 with the egg and forms an 

 oospore. The formation of 

 the oospore completes the 

 life of this, the sexual, gen- 

 eration of the fern. 



The oospore germinates 

 while still attached to the 

 httle prothallus, and from 

 it develops the large fern 

 plant with which we are 

 famihar. This second gen- 

 eration has true roots, 

 stems, and leaves, and on 

 the lower side of the leaves 

 great numbers of sporangia 

 are produced. These Ue in 

 groups which may be seen 

 with the naked eye as 

 brown dots. Within the sporangia asexual spores are formed, 

 and because asexual spores are produced by this generation, 

 it may be called the asexual generation of the plant. 



The ferns, therefore, do not reproduce themselves directly. 

 The plants with the large, feathery leaves that we know as 



Fig. 171. Underground stem, roots, and 

 leaves of fern. 



