STRUGGLE FOR EXISTENCE 109 



stances, increases inordinately in numbers in a small 

 tract, epi demicsr^ at least, this seems generally to occur 

 with our game animals — often ensue; and here we have a 

 limiting check independent of the struggle for life. But 

 even some of these so-called epidemics appear to be due 

 to parasitic worms, which have from some cause, possibly 

 in part through facility of diffusion among the crowded 

 animals, been disproportionally favored: and here comes 

 in a sort of struggle between the parasite and its prey. 

 On the other hand, in many cases, a large stock of 

 individuals of the same species, relatively to the numbers 

 of its enemies, is absolutely necessary for its preserva- 

 tion. Thus we can easily raise plenty of corn and rape- 

 seed, etc., in our fields, because the seeds are in great 

 ^ excess compared with the number of birds which feed 

 on them; nor can the birds, though having a superabun- 

 dance of food at this one season, increase in number 

 proportionally to the supply of seed, as their numbers 

 are checked during winter; but any one who has tried, 

 knows how troublesome it is to get seed from a few 

 wheat or other such plants in a garden: I have in this 

 case lost every single seed. This view of the necessity 

 of a large stock of the same species for its preservation, 

 explains, I believe, some singular facts in nature, such as 

 that of very rare plants being sometimes extremely abun- 

 dant, in the few spots where they do exist; and that of 

 some social plants being social, that is abounding in 

 individuals, even on the extreme verge of their range. 

 For in such cases, we may believe, that a plant could 

 exist only where the conditions of its life were so favor- 

 able that many could exist together, and thus save the 

 species from utter destruction. 1 should add that the 



