54 



ECOLOGY 



Part II 



fire is "alive" in so far as it is freeing energy gathered from the sun and stored 

 in plant cells millions of years ago. Neither coal nor diamonds are modern 

 upstarts: both have long been important to humanity, in fires for the tempering 

 and molding of metals, in various techniques, and in tokens and jewelry. 



Distribution. There are many ways in which plants depend upon animals. 

 Most animals can travel around freely; plants cannot. Plants are carried about 

 by the natural forces of air and water and by animals. Thus insects carry 

 pollen (male sex cells) and cross-pollinate the flowers as they seek nectar and 

 pollen in one after another (Fig. 4.3). Birds carry seeds across land and water 

 often to germinate safely in distant regions. Plants are directly dependent on 

 the content of the soil and animals fertilize this with their excretions and 

 disintegrating remains. 



Photosynthesis 



Green plants are, with exceptions such as nitrifying bacteria, the only self- 

 supporting organisms on the earth. They accumulate energy from the sun and 



Pathway of male cell 

 to the 



Pollen grains touch 

 stigmatic surface 



Fig. 4.3. The parts of a typical flower. Insects visit flowers to gather nectar and 

 pollen. The nectaries are at the bases of the petals and many flower-visiting insects 

 must brush against the pollen-bearing anthers in order to reach the nectar. In mov- 

 ing around they transfer the pollen containing the male cells to the stigma of the 

 flower or other flowers of the same kind and thus bring about the fertilization of 

 the ovules (eggs). 



