542 Length of the Fruit in Oenothera Lainarckiana. 



ably (the maximum increase being almost a third of the 

 original length). 



For the sake of further discussion, we may sum up 

 this result briefly in two theses : 



1. In both cases the length of the fruit increased. 



2. With the selection of a long-fruited seed-parent 

 this increase was considerably greater than when 

 a short-fruited one was selected. 



It is evident that the latter fact is simply the result 

 of selection. All the other conditions of the experiment- 

 were exactly the same, and the difference in the results 

 is exactly what one would expect as the result of selec- 

 tion. We need not therefore enter further into it. 



But it is a very different matter that the length of 

 the fruit increased in both cultures and especially that 

 this happened in the case of the choice of short-fruited 

 seed-parents. This cannot have been the result of selec- 

 tion, and the only other possible cause can have been the 

 heavy manuring of the parent-plant with horn-flour. 



In the long-fruited culture the mean fruit-length 

 (33.4 mm.) was larger than the corresponding value in 

 the seed-parent (32.6 mm.). The known principles of 

 selection, and particularly Galton's researches on re- 

 gression, make the interpretation of this result as the 

 effect of selection, impossible. Selection would, of course, 

 effect an increase in the length of the fruit, but the new 

 value would have to lie between the original mean and 

 the fruit-length of the seed-parent. Here however it 

 was greater than that of the seed-parent, and this can 

 only be ascribed to the heavy manuring of the parent- 

 plants.^ 



^ I have often observed this effect of the manuring of the parent- 

 plants in cuhures with other species, for example in Ranunculus 

 bulbosits in pleiopetaly. See the second volume. 



