STRUGGLE FOR EXISTENCE. 65 



hearts-ease and red clover would become very rare, or wholly 

 disappear. The number of humble-bees in any district 

 depends in a great measure upon the number of field-mice, 

 which destroy their combs and nests ; and Colonel Newman, 

 who has long attended to the habits of humble-bees, believes 

 that " more than two-thirds of them are thus destroyed all 

 over England." Now the number of mice is largely depend- 

 ent, as every one knows, on the number of cats ; and Colonel 

 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, act- 

 ing 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 dis- 

 tricts. When we look at the plants and bushes clothing 

 an entangled bank, we are tempted to attribute their pro- 

 portional 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 forests. 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 



