i 3 8 MENDELISM chap. 



sive generation. We are led, therefore, to the conclusion 

 that two sorts of variations exist, those which are due to 

 the presence of specific factors in the organism and those 

 which are due to the direct effect of the environment 

 during its lifetime. The former are known as mutations, 

 and are inherited according to the Mendelian scheme ; 

 the latter have been termed fluctuations, and at present 

 we have no valid reason for supposing that they are ever 

 inherited. For though instances may be found in which 

 effects produced during the lifetime of the individual 

 would appear to affect the offspring, this is not necessarily 

 due to heredity. Thus plants which are poorly nourished 

 and grown under adverse conditions may set seed from 

 which come plants that are smaller than the normal al- 

 though grown under most favorable conditions. It is 

 natural to attribute the smaller size of the offspring to the 

 conditions under which the parents were grown, and 

 there is no doubt that we should be quite right in doing 

 so. Nevertheless, it need have nothing to do with hered- 

 ity. As we have already pointed out, the seed is a larval 

 plant which draws its nourishment from the mother. 

 The size of the offspring is affected because the poorly 

 nourished parent offered a bad environment to the young 

 plant, and not because the gametes of the parent were 

 changed through the adverse conditions under which it 

 grew. The parent in this case is not only the producer of 

 gametes, but also a part of the environment of the young 



