The Inherited Effects of Changes 47 



eral generations to produce seeds all of which contain nearly 

 the maximum possible food supply. 



Suppose when this condition is attained we reverse the pro- 

 cess and plant the seeds under poorer conditions. The first 

 crop from such seeds will still be above the original average, 

 but not as much above as though they had grown under favor- 

 able conditions. Their seeds again will contain less nourish- 

 ment, and the second generation will be still smaller on the aver- 

 age, until finally the race reaches the lowest level shown by 

 fluctuating variations. 



The inheritance of the acquired character in these cases is 

 brought about in rather a peculiar way. The favorable exter- 

 nal conditions, for instance, act favorably on the body-cells of 

 the plant, and the germ-cells are therefore well nourished and 

 store up more food : not all to the same extent, but the average 

 is higher than in the preceding generation. The next genera- 

 tion thus gets a better start, and if the plants are better nourished 

 than the average, a similar advance is again made. We must 

 not forget that in each generation some of the seeds may be as 

 good as the best, but others are not as good. It is the average 

 that is improved, and not the best individual seed. 



It may appear from the case just given that the food condi- 

 tions determine only the size and vigor of the plant. This is 

 not the whole matter, for even the~ characters of certain parts 

 may be changed in a plus or a minus direction, provided they 

 are correlated with the condition of nourishment of the plant. 

 De Vries cites the case of the poppy, Papaver somniferum. In 

 this plant the stamens may be changed into supernumerary or 

 accessory carpels by changing the external conditions. The 

 number of these carpels may be as great as 1 50 or more. From 

 the seeds of flowers with an average crown of carpels, plants 

 may be reared having many or few of these organs. The more 

 favorable the conditions, the more numerous the carpels, and 

 vice versa. Poorly nourished plants may have only one or two 

 rudimentary or accessory carpels. 



If we select in each generation the most vigorous plants (hav- 



