CHAPTER XXIII 



Adaptation to the environment in plants Alpine plants, desert plants and 

 lianes The modification of flowers in relation to insect-fertilization. 



IN plants no less than in animals we find adaptation to the 

 conditions under which they have to live to be the most striking 

 feature of their organization. We have already noticed, in 

 dealing with the phenomenon of convergent evolution, the 

 manner in which Alpine plants of many kinds tend to assume the 

 compact cushion-like form which seems best suited to withstand 

 the rigorous climate to which they are exposed. Wherever a 

 plant may be found growing in a state of nature the character of 

 the environment is sure to be reflected more or less obviously in 

 its structure arid habit. We see this equally clearly in the 

 water-storing plants of desert regions the cacti of America 

 or the aloes of Africa with their succulent stems or leaves and 

 other structural modifications which enable them to withstand 

 the effect of long-continued drought, and in the climbing lianes 

 of tropical forests, whose one object in life appears to be to reach 

 some elevation where they can expose their foliage to the light 

 and air. Just as we find those air-breathing mammals which 

 have taken to an aquatic life adopting the form and habits of 

 fishes as being best suited to their changed conditions, so in the 

 tropical forests of Queensland we find palms, members of a group 

 which elsewhere are types of self-supporting independence, 

 adopting the form and habit of climbing plants as the only means 

 of coping with the exigencies of the situation. 



If the adaptation amongst plants usually appears less remark- 

 able than is often the case in animals, it is because the 

 relations of a plant to its environment are usually less complex 

 than those of an animal. The greater activity of animals is 

 associated with the development of highly specialized organs of 

 locomotion, sense-organs and nervous system, all of which are 

 alike subject to adaptation. Plants afford much more restricted 

 opportunities for the effects of the environment to show them- 

 selves, and it is in their relations with animals, or to speak more 



