54 STRUGGLE FOR EXISTENCE. [CHAP. HI. 



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 different 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 beautiful 

 diversity and proportion of kinds as 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 ; what war between insect and insect 

 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 seedlings, or on the other plants which 

 first clothed the ground and thus checked the growth of the 

 trees ! Throw up a handful of feathers, and all fall to the ground 

 according to definite laws ; but how simple is the problem where 

 each shall fall compared to that of the action and reaction of the 

 innumerable plants and animals which have determined, in the 

 course of centuries, the proportional numbers and kinds of trees 

 now growing on the old Indian ruins ! 



The dependency of one organic being on another, as of a 

 parasite on its prey, lies generally between beings remote in the 

 scale of nature. This is likewise sometimes the case with those 

 which may be strictly said to struggle with each other for 

 existence, as in the case of locusts and grass-feeding quadrupeds. 

 But the struggle will almost invariably be most severe between 

 the individuals of the same species, for they frequent the same 

 districts, require the same food, and are exposed to the same 

 dangers. In the case of varieties of the same species, the struggle 

 will generally be almost equally severe, and we sometimes see 

 the contest soon decided : for instance, if several varieties of wheat 

 be sown together, and the mixed seed be resown, some of tk 



