NATURE OF PLANTS 129 



it will develop into a plant that will show various associations 

 of the parental characters. It is possible 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 

 watch the changes in vegetation that occur in the cultivated field 

 that is allowed to remain fallow for several years. Each suc- 

 ceeding year will mark the crowding out of certain forms by 

 plants that possess variations that better adapt them to the locality. 

 These changes in the vegetation will go on until the forms are 

 introduced whose special variations adapt them to the conditions 

 of the field and to the competition of the other plants. This 

 vegetation of the field is now fixed owing to the survival of the 

 fit. In this way the distribution and association of the vegeta- 

 tion of the earth has been brought about. 



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