80 STRUGGLE FOK EXISTENCE. Chap. ^ly, 



the nests of humble-bees more numerous than elsewhere, Mhich 

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

 it is quite credible that the presence of a fefine animal in large 

 numbers in a district might determine, through the interven- 

 tion 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 diflerent 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 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 

 jilants and bushes clothing an entangled bank, Ave 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 differ- 

 ent vegetation springs up ; but it has been observed that an- 

 cient Indian ruins in the Southern United States, which must 

 formerly haA'e been cleared of trees, now display the same 

 beavitiful diversity and proportion of kinds as in the surround- 

 ing virgin forest. What a struggle must have gone on during 

 long centuries betAveen the scA'cral kinds of trees, each annual- 

 ly scattering its seeds by the thousand ; Avhat Avar betAvcen 

 insect and insect — between insects, snails, and other animals, 

 Avith birds and beasts of pre}^ — all striving to increase, ail 

 fcx'ding on each other, or on the trees, their seeds and seed- 

 lings, or on the other plants Avhich first clothed the groimd 

 and thus checked the groAvth of the trees ! ThroAV vip a handful 

 of feathers, and all must fall to the ground according to defi- 

 nite laAvs ; but Iioav simple is the jiroblem Avhere each shall fall 

 compared to that of the action and reaction of the innumerable 

 plants and animals which haA'C determined, in the course of 

 centuries, the proportional numbers and kinds of trees noAV 

 ffroAving on the old Indian ruins ! 



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

 parasite on its prey, lies generally betAveen beings remote in 

 the scale of nature. This is likcAvise sometimes the case Avith 

 those Avhich may strictly be said to struggle Avith each other 

 for existence, as in the case of locusts and grass-feeding quad- 

 rupeds. But the struggle Avill almost invariably be most 

 severe betAveen the individuals of the same species, for they 

 frequent the same districts, require the same food, and are 



