440 THE RESULTS OF EVOLUTION 



the other hand, where the light and heat are intense, 

 as in the tropics or deserts, the leaves of many plants 

 close and bend downward, thus escaping the danger of 

 excessive illumination and evaporation. Other plants 

 undergo somewhat similar nocturnal movements and 

 prevent an undue loss of heat. 



Another phase of adjustment appears in the case of 

 those plants capable of existing amid markedly different 

 surroundings. Individuals, even from the same parent, 

 if grown in very moist habitats, differ materially from 

 those in comparatively dry soil. Those of cold elevated 

 regions are decidedly unlike their brothers of the lowlands. 

 And furthermore, while these plants of the mountain top 

 or cold countries die down in the fall, the very same 

 plants in warmer regions, in many instances, may live 

 for several years. 



Every plant and every organ of the plant is thus a 

 delicately adjusted mechanism under the sway of many 

 controlling influences. Heat, light, moisture, soil condi- 

 tions, gravity, etc., are continually stimulating the living 

 material, which responds by molding its leaves, stems, or 

 roots to harmonize with or fit into the shifting conditions. 



Colors of Animals. — One of the most universal feat- 

 ures of living things is their color. In many instances 

 this obviously is an adaptation; in certain other cases 

 its significance at the present time is by no means 

 clear. The re(hiess of the blood, for example, is 

 seemingly an incidental result of its chemical com- 

 position, and is of no more use to the organism than 

 color is to a brick or a ten cent piece. On the other 

 hand, there are very many species where the color pattern 

 is believed to be of the highest value in the struggle for 

 existence. It may serve so to blend an animal with its 

 surroundings that it escapes the notice of enemies, or it 

 may enable it to steal unobserved upon its prey. In other 

 animals it apparently is of service in giving warning to 

 friends or, in still other species, to foes. And finally it 



