88 ORIGIN OF SPECIES 



became extinct or very rare in England, the heartsease 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 Col. Newman, who has long 

 attended to the habits of humble-bees, believes that "more 

 than two-thirds of them are thus destroyed all over Eng- 

 land." Now the 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 ani- 

 mal in larje numbers in a district might determine, through 

 the intervention first of mice and then of bees, the fre- 

 quency 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 deter- 

 mining 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 sev- 

 ' eral 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 



