THE STRUGGLE FOR EXISTENCE 895 
often decide which plant or plants of any particular 
kind shall live and which ones shall die out. In every 
grove of oaks there are some with sweeter and others with 
more bitter acorns. One shellbark hickory bears nuts 
whose shell is easily cracked by hogs, while another pro- 
tects its seeds by a shell so hard that it is cracked only 
by a pretty heavy blow. In case of all such differences, 
there is a strong tendency to have the less eatable fruit or 
seed preserved and allowed to grow, while the more eat- 
able varieties will be destroyed. Some individuals of the 
European holly produce bright red berries, while others 
produce comparatively inconspicuous yellow ones. It has 
been found that the red berries are much more promptly 
carried off by birds, and the seeds therefore much more 
widely distributed than the yellow ones are. The result 
of this kind of advantage, in any of its countless forms, is 
sometimes called survival of the fittest, and sometimes 
natural selection. ‘The latter name means only that the 
outcome of the process just described, as it goes on in 
nature, is much the same as that of the gardenev’s selection, 
when, by picking out year by year the earliest ripening 
peas or certain kinds of the oddest-colored chrysanthe- 
mums, he obtains permanent new varieties. Natural 
agencies, acting on an enormous scale through many 
ages, may well be supposed to have brought about the 
perpetuation of millions of such variations as are known 
to be of constant occurrence among plants, wild as well 
as cultivated. 
