REPRODUCTION: ALTERNATION OF GENERATIONS 277 



and becomes surrounded by a hard shell, inside of which it 

 remains dormant for an indefinite period. This forms the 

 seed, which thus appears to be a little sporophyte surrounded 

 by a shell, and it remains dormant until later when it can be 

 placed under proper conditions for germination; Fig. 66. It 

 develops its spores, of course, after it has grown large enough 

 to produce flowers. 



It is thus seen that the flowering plant has an alternation 

 of generations as truly as does the fern, only in the flowering 

 plant the sex stage, the gametophyte, is very small, while the 

 asexual stage is very large. The plant with which we are 

 familiar is in the sporophyte stage, and the pollen and the 

 single cell inside its ovule are its spores. These develop into 

 tiny growths that correspond to the gametophytes and are 

 developed within, or attached to, the sporophyte that produced 

 the spores, i. e., in the ovary or attached to the stigma. But 

 tiny as they are, they produce the equivalents of eggs and 

 sperms, which subsequently fuse by true fertilization. The real 

 fertilization of the plant, then, is the fusion of the male cell 

 contained in the pollen tube with the egg contained in the 

 ovule. The term fertilization, which has been commonly ap- 

 plied to the transfer of the pollen to the stigma, is a misnomer, 

 and is largely given up, the term pollination being substituted 

 instead. 



Alternation of Generations among Animals. An alternation 

 of generations also occurs in the animals known as hydroids, 

 animals related to the Hydra. The fresh-water Hydra, as 

 described in Chapter VII, multiplies by budding; but as fast 

 as the buds are produced they break away from the original 

 animal and become independent. In the marine Podocoryne, 

 the buds do not break away but remain attached to form a 

 colony, made up of large numbers of individuals; Fig. 129. 

 The individuals are partially independent of each other and. 

 if broken apart are capable of living independent lives. This 

 stage of the life of the animal, since it has an asexual multi- 



