440 



Minnesota Plant Life. 



Intra-specific adaptations. A last group of adaptations 

 that may be considered here are those connected with spore 

 distribution and seed distribution. It is necessary for the well 

 being of the species that new individuals should be given an 

 opportunity to develop. Thus arose such simple primitive 

 adaptations as the elongation of the spore-bearing plant in 

 mosses and liverworts, so that the spores could be distributed 

 over a wider area. More perfected apparatus enabled the 

 spores to be distributed under conditions of moisture such that 

 they would most certainly germinate. As spores assumed a 

 division of labor, devices were adopted by which the two sexual 

 plants might be produced close together, thus insuring fecun- 

 dation of the eggs. The ancestors of the seed-bearing plants 

 originated methods of keeping the young embryo close to the 

 vegetative areas of the preceding individuals in the species line. 

 In this manner there arose in the plant kingdom such complex 

 structures as flowers and seeds. With the added complexity 

 of structure it became possible for a great number of slight 

 differences in detail to exist and thus the highest division of 

 the plant world, that of the seed-bearing plants, is also the one 

 in which the greatest number of different species are described. 

 A vast number of intricate adaptations for pollination, embryo- 

 nursing, and seed distribution came into existence. In some 

 families of plants wind pollination, or wind distribution of seed, 

 became the rule, while in others the seeds are distributed by 

 animals and the pollen spores are planted on the stigma of the 

 flower by the same animate agents. All the manifold variety 

 of form in flowers and fruits may be regarded as due to adapta- 

 tions, more or less perfect, by which the two sexes of plants are 

 developed sufficiently near together, by which the young plants 

 may derive benefit from supplies of nourishment produced by 

 maturer individuals of their species, or by which they are placed 

 under conditions favorable for their growth and for the best 

 interests of the species as a whole. 





