On the Inheritance of Acquired Characters. 135 



richer are its inflorescences in marginal florets. But the 

 luxuriance of the plant is the direct result of nutrition, 

 and we cannot escape the conclusion that the same is true 

 of the marginal florets. And the same rule applies to the 

 whole organization of the plant. -^ 



Our conclusion is therefore that we have two cat- 

 egories of characters, one which includes mutations only ; 

 and another which includes "acquired characters," nu- 

 tritional modifications and individual variations. The 

 only difference between true individual variations and 

 these modifications is that the latter are determined in a 

 more evident manner bv external conditions. 



§ i6. ON THE INHERITANCE OF ACQUIRED CHAR- 

 ACTERS. 



Herbert Spencer is more than any one else re- 

 sponsible for the doctrine of acquired characters." He 

 starts with the belief, based on general observation, that 

 the differences between the individuals of a species are 

 caused by the conditions in which they live and that 

 such dift'erences are inherited. 



We have seen in the preceding sections how ac- 

 quired characters manifest themselves as individual devi- 

 ations from the mean character of the type in question. 

 The question of their inheritance must therefore be 

 judged from this point of view. 



The inheritance of individual variations differs from 

 that of mutations in that the former exhibits the phe- 

 nomena of regression and of accumulation by selection. 



^ J. Mac Leod, Over de veranderlykheid van hcf aantal rand- 

 bloemen by de Korenbloem. Handelingen Vlaam.sch Natuiirk. Con- 

 gres, 1899. 



" See especially his various essays in The Contemporary Review. 



