UNIVERSALITY OF VARIATION. 1 57 



quite universal ; we must necessarily assume it even where, 

 with the imperfect capabilities of our senses, we are unable 

 to discover differences. Among the higher plants (the 

 phanerogams, or flower-plants), where the individual stocks 

 show such numerous differences in the number of branches or 

 leaves, and in the formation of the stem and branches, we 

 can almost always easily perceive these differences. But 

 this is not the case in the lower plants, such as mosses, 

 algse, fungi, and in most animals, especially the lower ones. 

 The distinction of all the individuals of one species is here, 

 for the most part, extremely difficult or altogether impossible. 

 ' But there is no reason for ascribing individual differences only 

 to those organisms in which we can perceive them at once. 

 We may, on the contrary, with full certainty assume such 

 individuality as a universal quality of all organisms, and we 

 can do this all the more surely since we are able to trace the 

 mutability of individuals to the mechanical conditions of 

 nutrition. We can show that by influencing nutrition we 

 are able to produce striking individual differences where they 

 would not exist if the conditions of nutrition had not been 

 altered. The many complicated conditions of nutrition are 

 never absolutely identical in two individuals of a species. 



Now, just as we see that the mutability or capability of 

 adaptation has a causal connection with the general rela- 

 tions of nutrition in animals and plants, so too we find the 

 second fundamental phenomenon of life, with which we are 

 here concerned, namely, the capability of transmitting by 

 inheritance, to have a direct connection with the phenome- 

 non of propagation. The second thing that a farmer or 

 gardener does in artificial breeding, after he has selected, 

 and has consequently availed himself of the mutability, is 



