216 



A TEXT-BOOK OF BOTANY 



203, D). Such a gametophyte has become so small that 

 it can be seen only under the microscope. Among the 



cells formed, however, 

 are two sperms. These 

 sperms have no cilia, and 

 hence it is evident that 

 they do not reach the egg 

 by swimming. 



The single large spore 

 within the ovule (spo- 

 rangium) is peculiar in 

 never leaving it; that is, 

 it is never shed, as are 

 other spores. It pro- 

 duces a many-celled fe- 

 malegametophytejustas 

 does Selaginella ( 118); 

 and on this gametophyte 

 archegonia are formed 

 (Fig. 205). Since the 

 large spore is not shed, 

 the female gametophyte 

 it produces lies embed- 

 ded in the center of the 

 ovule, like an internal 

 parasite (Fig. 205, </). 

 It is evident now why the gametophytes of such plants 

 are not ordinarily seen, for one is within the pollen grain 

 and the other is within the ovule. 



125. Fertilization. Before fertilization can take place, 

 the pollen grain, which develops the male gametophyte with 

 its sperms, must be brought to the ovule, which contains 

 the female gametophyte with its archegonia. The pollen 

 grains (microspores) are formed in very great abundance, 

 are dry. and powdery, and are scattered far and wide by 



Fia. 205. A, section showing the relative po- 

 sitions of bract (6), scale (s), and ovule (o) 

 in a pine cone, the female gametophyte (g) 

 being very young; B, enlarged section 

 through the ovule a year later, showing the 

 female gametophyte (g) bearing two arche- 

 gonia (a) which are being reached by the 

 penetrating pollen tubes (0. 



