434 Life and Immortality. 
necessity of a large stock of the same species for its pres- 
ervation, for in such cases we may believe that a plant could 
only exist where the conditions of its life were so favorable 
that many could exist together and thus save the species from 
extinction. 
Complex and varied are the checks and relations between 
organic beings which have to struggle together in the same 
country. In the case of every species, many different 
checks, some very complicated and unintelligible to man at 
present, acting at different periods of life, and during different 
seasons or years, come into play, some one check or some 
few being generally the most powerful, but all concurring 
in determining the average number or even the existence 
of the species. Widely-different checks sometimes act on 
the same species in different districts. Looking at the 
plants and bushes that clothe an entangled bank, we are 
tempted to ascribe their proportional numbers and kinds to 
what we call chance. But this is a very false view to take 
of the matter. Chance has no part in such things. They 
follow in obedience to laws of which we know comparatively 
little. When an American forest is cut down a very different 
vegetation springs up. Ancient Indian ruins have been 
observed in the southern parts of the United States, which 
must in former times have been cleared of trees, but which 
now display the same beautiful diversity and proportion of 
kinds as are now found in the surrounding virgin forest. 
What a struggle must have gone on during long centuries 
between the several kinds of trees, each annually scattering 
its seeds by the thousand, and what a war between insect 
and insect, and between insects, snails and other animals 
with birds and beasts of prey, all striving to increase, all 
feeding on each other, or on the trees, their seeds and their 
seedlings, or on the other plants which once clothed the soil, 
and thus checked the growth of the trees! It is easier to 
account for the fall of an apple from a tree, or the descent 
of a stone to the earth when hurled into the air, than to 
