Chap, in.] STEUGGLE FOR EXISTENCE. 91 



number of mice is largely dependent, as every one 

 knows, on the number of cats ; and Col. Newman says, 

 " Near villages and small towns I have found the nests 

 of humble-bees more numerous than elsewhere, which I 

 attribute to the number of cats that destroy the mice." 

 Hence it is quite credible that the presence of a 

 feline animal in large numbers in a district might 

 determine, through the intervention first of mice and 

 then of bees, the frequency of certain flowers in that 

 district ! 



In the case of every species, many different checks, 

 acting at different periods of life, and during different 

 seasons or years, probably come into play ; some one 

 check or some few being generally the most potent ; 

 but all will concur in determining the average number 

 or even the existence of the species. In some cases it 

 can be shown that widely-different checks act on the 

 same species in differ en t districts. When we look at 

 the plants and bushes clothing an entangled bank, we 

 are tempted to attribute their proportional numbers and 

 kinds to what we call chance. But how false a view is 

 this ! Every one has heard that when an American 

 forest is cut down, a very different vegetation springs 

 up ; but it has been observed that ancient Indian ruins 

 in the Southern United States, which must formerly 

 have been cleared of trees, now display the same beau- 

 tiful diversity and proportion of kinds as in the sur- 

 rounding 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; what war between insect and insect — 

 between insects, snails, and other animals with birds 

 and beasts of prey — all striving to increase, all feeding 



