DAME NATURE AND HER CHILDREN 



bivorous and graminivorous mammals greatly exceed 

 in numbers the flesh-eaters; they can get their food 

 more easily, for they do not have to use speed, wit, 

 strength, or prowess hi order to obtain it. How rare 

 are the weasels, compared with their prey of rats 

 and mice and birds and squirrels and rabbits ! Yet 

 the weasels have goodly families each season. If 

 man had not been a miscellaneous feeder, could he 

 have overspread the earth as he has done? If an 

 animal can eat only fish, it must keep near the water; 

 if it can eat only nuts, it must keep near the woods; 

 if it subsists upon mosquitoes, it must live near the 

 marshes; if grass is its only diet, its range is limited 

 to certain zones and certain seasons. 



The farmer finds it much more difficult to check 

 or exterminate certain plants or weeds than others. 

 The common milkweed and the Canada thistle defy 

 his plough because the parent roots are beyond its 

 reach; they creep horizontally through the soil, and 

 send up their shoots at short intervals. To exter- 

 minate the plants, you must remove the parent 

 roots. Looked at in the light of the doctrine of 

 natural selection, it would seem as if these two 

 plants had learned through experience to avoid the 

 plough by diving deeper into the soil and establish- 

 ing permanent parent roots there. This method or 

 habit baffles the plough completely. What other 

 enemy or circumstance could have so driven them 

 into the ground? In a region unvisited by the 

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