CHAPTER X 



THE ADAPTATION OF ORGANISMS TO THEIR 

 ENVIRONMENT 



WE may now look briefly at the general relations of 

 organisms to their environment, how they adapt them- 

 selves to their surroundings, making the best of such 

 as are favourable to their healthy existence and the 

 multiplication of their offspring, and protecting 

 themselves from such as are injurious to them or 

 their progeny. Let us, first of all, look at plant 

 life, and here, at the outset, we meet with differences 

 once more dependent on the fact that the plant is a 

 fixed organism while the animal is pre-eminently 

 a motile one. Manifestly, we may expect the plant 

 to show more adaptability than the animal, simply 

 because the animal, in virtue of its locomotory 

 powers, can remove itself from obnoxious influences, 

 while the plant cannot escape, and must therefore 

 adapt itself, temporarily or permanently, to its 

 surroundings or succumb. 



Before going into the consideration of specific 

 examples, let us briefly summarise the principal 

 external influences which affect plants. 



First, we have what may be termed mechanical 



influences of the environment, represented by 



amount of space, lateral or vertical pressures 



Nature and tensions, and so on; then we have chemical 



vfrormfent. influences, such as those of food, air, water, the 



nature of the medium in which the organism lives, 



&c. ; thirdly, physical influences, which we may 



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