334 



REPRODUCTION IN PLANTS 



times the diameter of the small spore and consequently 

 contain from five hundred to a thousand times (i.e., 8* 

 or 10^) as much substance. When they germinate they 

 develop into small fe/male gametophytes, which are 

 almost wholly enclosed within the spore wall (Fig. 88). 

 This differentiation of spores in respect to size and the 

 retention of the gametophytes within the spore wall led 



Fio. 88. — iSelaidnella. 1. a megaspore containing a mature full- 

 grown female gametophyte with several archegonia exposed through 

 the ruptured spore coat. 2. a young sporophyte which has developed 

 from an egg fertilized in such an archegonium as shown in the pre- 

 ceding figure. Note that this young plant remains attached for a 

 considerable time to the female plant and draws its food from the 

 supply originally stored in the large spore. («p) the old spore, 

 (r) the first root of the new sporophyte, («/) and (/) the young stem 

 and leaves. 3 and 4. older stages of the young plant. (Reproduced 

 by permission from drawings by Professor Campbell.) 



to the further development, along the same lines, of the 

 pollen and seeds of higher plants. 



Reproduction by Seed is a specialized development of 

 the alternation of generation. If one examines a flower 

 (Fig. 89) it will be found to be composed of an outer 



