274 GENERAL BIOLOGY 



the young is found in the birds, nearly all of which 

 display this characteristic to a greater or less degree. 

 Some sea birds lay their eggs on the bare rocks and 

 pay no more attention to them thereafter. The 

 majority of birds, however, build some sort of a 

 nest, and in some cases this is of elaborate design. 

 In many cases botjj male and female share the labor 

 of brooding the eggs and bringing food to the fledg- 

 lings. 



Environmental Adaptations of Plants. Since 

 plants have not the advantage animals enjoy of 

 moving from place to place, they are profoundly 

 modified by the nature of the soil in which they 

 grow. If this is rich and fertile, their growth is 

 luxuriant; if dry and poor, they are stunted, and the 

 aspect of two regions may differ very greatly on 

 this account. Temperature also plays an important 

 part, the vegetation of the arctics and of alpine 

 regions being also stunted in comparison with the 

 more luxuriant growth of warmer regions. But 

 the abundance or scarcity of water probably plays 

 the most significant role in determining the character 

 of the vegetation in any region. 



As previously noted, the plant world probably 

 took its origin in the water and secondarily migrated 

 to the land. Large groups, however, are still 

 confined to the former medium. These constitute 

 the familiar type of the water plants or hydrophytes. 

 They are characterized by soft and succulent tis- 

 sues with scant supporting tissue, since they are 



