REPRODUCTION IN PLANTS 



105 



prothallus from which its food is secured. Later, when direct 

 communication with the environment has been established 

 by its own root and leaf, the new generation becomes entirely 

 independent of the prothallus, which then degenerates and 

 dies. The young plant gradually grows into the typical 

 asexual leafy fern plant, which itself in due time produces 

 spores. 



It is clear that in the Fern, as in the Moss, there is an al- 

 ternation of generations. The leafy fern plant (sporophyte) 

 gives rise to the prothallus (gametophyte) . The leafy fern 



Ferns Flowering Plants 



Fio. 55. Diagram to illustrate the decline of the gametophyte generation 

 and the advance of the sporophyte generation. (From Coulter.) 



arises sexually, but is itself asexual; the prothallus arises 

 asexually, but is itself sexual. The significant fact, however, 

 is that the conspicuous leafy moss plant is a gametophyte, 

 while the large leafy fern plant is a sporophyte; or, one 

 may say, the 'moss' is a sexual plant and the 'fern' is an 

 asexual plant. This ascendancy in dominance of the asexual 

 and suppression of the sexual generation, which is so charac- 

 teristic of the fern as compared with the moss life history, is 

 carried still further in the higher Ferns and finally culminates 

 in the Flowering Plants. (Fig. 55.) 



3. Higher Ferns 



As we have seen, the sporophyte of the common Ferns pro- 

 duces spores on ordinary vegetative fronds or, more rarely, on 

 specialized sporophylls. (Figs. 39, 54.) In either case but one 



