THE STRUGGLE FOR EXISTENCE. 85 



much extinction, explains the arrangement of all the 

 forms of life in groups subordinate to groups, all within 

 a few great classes, which has prevailed throughout all 

 time. This grand fact of the grouping of all organic 

 beings under what is called the Natural System is utterly 

 inexplicable on the theory of creation. 



OBSCTTEE CHECKS TO INCREASE. 



Origin of ^^^ causes which check the natural tend- 



Species, ency of each species to increase are most ob- 

 P*^* ■ scure. Look at the most vigorous species ; by 

 as much as it swarms in numbers, by so much will it 

 tend to increase still further. We know not exactly what 

 the checks are even in a single instance. Nor will this 

 surprise any one who reflects how ignorant we are on this 

 head, even in regard to mankind, although so incompar- 

 ably better known than any other animal. 



Eggs or very young animals seem generally to suffer 

 most, but this is not invariably the case. With plants 

 there is a vast destruction of seeds, but, from some obser- 

 vations which I have made it appears that the seedlings 

 suffer most from germinating in ground already thickly 

 stocked with other plants. Seedlings, also, are destroyed 

 in vast numbers by various enemies ; for instance, on a 

 piece of ground three feet long and two wide, dug and 

 cleared, and where there could be no choking from other 

 plants, I marked all the seedlings of our native weeds as 

 they came up, and out of 357 no less than 395 were de- 

 stroyed, chiefly by slugs and insects. If turf which has 

 long been mown, and the case would be the same with 

 turf closely broTVsed by quadrupeds, be let to grow, the 

 more vigorous plants gradually kill the less vigorous, 



