STRUGGLE FOR EXISTENCE 91 



for diving, allows it to compete with other aquatic insects, 

 to hunt for its own prey, and to escape serving as prey to 

 other animals. 



The store of nutriment laid up within the seeds of many 

 plants seems at first sight to have no sort of relation to 

 other plants. But from the strong growth of young plants 

 produced from such seeds, as peas and beans, when sown in 

 the midst of long grass, it may be suspected that the chief 

 use of the nutriment in the seed is to favour the growth of 

 the seedlings, whilst struggling with other plants growing 

 all around. 



Look at a plant in the midst of its range, why does it not 

 double or quadruple its numbers? We know that it can per- 

 fectly well withstand a little more heat or cold, dampness or 

 dryness, for elsewhere it ranges into slightly hotter or colder, 

 damper or drier districts. In this case we can clearly see 

 that if we wish in imagination to give the plant the power of 

 increasing in number, we should have to give it some ad- 

 vantage over its competitors, or over the animals which prey 

 on it. On the confines of its geographical range, a change 

 of constitution with respect to climate would clearly be an 

 advantage to our plant ; but wc have reason to believe that 

 only a few plants or animals range so far, that they are de- 

 stroyed exclusively by the rigour of the climate. Not until 

 we reach the extreme confines of life, in the Arctic regions 

 or on the borders of an utter desert, will competition cease. 

 The land may be extremely cold or dry, yet there will be 

 competition between some few species, or between the indi- 

 viduals of the same species, for the warmest or dampest 

 spots. 



Hence we can see that when a plant or animal is placed 

 in a new country amongst new competitors, the conditions 

 of its life will generally be changed in an essential manner, 

 although the climate may be exactly the same as in its 

 former home. If its average numbers are to increase in its 

 new home, we should have to modify it in a different way to 

 what we should have had to do in its native country; for we 

 should have to give it some advantage over a different set 

 of competitors or enemies. 



It is good thus to try in imagination to give to any one 



