62 STRUGGLE FOR EXISTENCE. 



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

 viduals of the same species, relatively to the numbers of its 

 enemies, is absolutely necessary for its preservation. Thus 

 Ave 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 superabundance of food at this one 

 season, increase in number proportionally to the supply of 

 seed, as their numbers are checked during the 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 preser- 

 vation, explains, I believe, some singular facts in nature, 

 such as that of very rare plants being sometimes extremely 

 abundant, 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 favorable that manv 

 could exist together, and thus save the species from utter 

 destruction. I should add that the good effects of inter- 

 crossing, and the ill effects of close interbreeding, no, 

 doubt come into play in many of these cases ; but I will not 

 here enlarge on this subject. 



COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO 

 EACH OTHER IN THE STRUGGLE FOR EXISTENCE. 



Many cases are on record showing how complex and unex- 

 pected are the checks and relations between organic beings, 

 which have to struggle together in the same country. I 

 will give only a single instance, w T hich, though a simple 

 one, interested me. In Staffordshire, on the estate of a 

 relation, where I had ample means of investigation, there 

 was a large and extremely barren heath, which had never 

 been touched by the hand of man ; but several hundred 

 acres of exactly the same nature had been enclosed twenty- 

 live years previously and planted with Scotch fir. The change 

 in the native vegetation of the planted part of the heath 

 was most remarkable, more than is generally seen in pass- 

 ing from one quite different soil to another : not only the 

 proportional numbers of the heath-plants were wholly 

 changed, but twelve species, of plants (not counting grasses 



