UNIVERSALITY OF VARIATION. 157 
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, 
algze, 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 
imheritance, 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 
