NATURE OF PLANTS 137 



influenced by the stimuli of its environment. Gager has recently 

 shown that marked variations may be induced in the offspring 

 of Oenothera by subjecting the parents to the emanations of 

 radium and MacDougal reports like results from injecting solu- 

 tions into the ovaries. It seems altogether probable that the 

 hereditary substances may be similarly affected by the varied 

 stimuli which the plant is constantly receiving in nature. 



Later in the work it will be seen that nearly all plants have 

 devices of various kinds that assist in the transfer of the micro- 

 spores of one plant to the stigmas of other plants. In this way 

 the sexual generations that have been derived from plants that 

 may differ more or less from one another are brought together. 

 All these differences in so far as they are due to the hereditary 

 substances must be transmitted to the gametospore, consequently 

 it will develop into a plant that will show various associations 

 of the parental characters. We know that many kinds of plants 

 which we call species have arisen in this way. Mutations may 

 also have produced species and also lead to more pronounced 

 changes in the offspring which we recognize as genera. 



This brief consideration will give us an idea of the nature of 

 variation and it also helps us to understand the significance of 

 the elaborate processes leading up to fertilization. The varia- 

 tions and departures of the offspring from the parental type are 

 of great importance. In this way new characters arise that en- 

 able the offspring to live under conditions that the parents can 

 not endure, consequently the offspring can occupy territory that 

 would not support the parents and as a result they do not come 

 into competition with them. Variations have gone on from one 

 cause or another during the past ages and thus plants have be- 

 come adapted to practically all the different conditions of soil 

 and climate on the face of the earth. It must also be borne in 

 mind that these variations may adapt a wide variety of plants 

 to one and the same condition. Consequently in every locality 

 we find plants living together and fiercely competing for their 

 existence. Here again it is the variation of each kind of plant 

 that gives it a slight advantage and enables it to compete success- 

 fully with its associates or supplant them. It is instructive to 



