72 ORGANIC EVOLUTION 



The relation of soma and germ cells in plants and the 

 relation of the germ substance to the processes of regenera- 

 tion in plants are more obscure than the similar relations in 

 animals. It does not seem best to attempt to discuss them 

 here. 



The modifications of the sown, to which we must refer, 

 are of two sorts, first, those produced by the effect of the 

 environment upon the organism, and, second, those resulting 

 from the reaction upon itself of the activity of the animal 

 or plant. Let us illustrate each. 



The direct influence of food and climate is often of such 

 a nature as to produce changes in the individual. For exam- 

 ple, plants, if grown in a warm moist climate and in rich soil, 

 may be larger than if grown under less favorable circum- 

 stances. Will these plants have larger offspring as a result 

 of inheritance of the increased size? Is the direct effect 

 of the favorable environment (increased size) handed down 

 to the offspring? If the offspring be large, as they probably 

 will be, is their large size due to the fact that their parents 

 became laro-e under the favorable conditions in the midst of 



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which they grew, or to the fact that the offspring themselves 

 grow under the same favorable conditions as their parents 

 and so, for this reason, are large ? That is, is their size 

 clue to the inheritance of the increased size of their 

 parents, or to the same favorable soil and climate that made 

 their parents large? Is there at all any inheritance of 

 increased size? How can we tell? We have at least one 

 test which we may apply. When plants are taken from 

 unfavorable conditions and are grown under the most favor- 



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able conditions, do they only gradually assume increased size, 

 or are those of the first or second generation as large as 



