56 STKUGGLE FOR EXISTENCE. [CHAP. IIL 



on which it preys. This is obvious in the structure of the teeth 

 and talons of the tiger ; and in that of the legs and claws of the 

 parasite which clings to the hair on the tiger's body. But in the 

 beautifully plumed seed of the dandelion, and in the flattened and 

 fringed legs of the water-beetle, the relation seems at first confined 

 to the elements of air and water. Yet the advantage of plumed 

 seeds no doubt stands in the closest relation to the land being 

 already thickly clothed with other plants ; so that the seeds may 

 be widely distributed and fall on unoccupied ground. In the 

 water-beetle, the structure of its legs, so well adapted 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 vigorously all around. 



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

 or quadruple its numbers 1 We know that it can perfectly well 

 withstand a little more heat or cold, dampness or dryness, for else- 

 where 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 advantage over its competitors, or 

 over the animals which prey on it. On the confines of its geo- 

 graphical range, a change of constitution with respect to climate 

 would clearly be an advantage to our plant ; but we have reason 

 to believe that only a few plants or animals range so far, that they 

 are destroyed 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 laud 

 may be extremely cold or dry, yet there will be competition between 

 some few species, or between the individuals 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 

 species an advantage over another. Probably in no single instance 



