INTRODUCTORY 5 



in length. Some very pure natural waters contain no plants 

 readily visible to the eye, while the foul drainage of a barn- 

 yard in warm weather may be of a uniform bright-green color 

 from the presence of many thousands of microscopic plants 

 in every drop of the water. Plants occur in all the seas as 

 well as in all the fresh waters, on every kind of soil from the 

 wettest swamps to arid deserts, on rocky cliffs, and on 

 branches and leaves of trees. 



4. Structures and habits of plants. Although the relations 

 of plants to human life and the life of the lower animals are 

 of the highest importance, it is not this aspect of botany which 

 is of largest concern to the beginner. We have no reason to 

 suppose that plants exist for the benefit of man. Plant struc- 

 tures and processes are of importance primarily in maintaining 

 the life of plants themselves, and their use by men is a by- 

 product of plant life. In order to gain any scientific knowl- 

 edge of elementary botany, it is necessary to try to find out 

 what are the forms and internal structures of plants, how they 

 carry on their life processes, and what relations exist between 

 them and the external conditions of soil and climate. To these 

 studies may be added some consideration of the relations be- 

 tween the plant and its plant and animal neighbors, and other 

 studies about what plants have done for man and what he is 

 trying to do with plants. But it must be clearly understood 

 that the study of plant structures and functions what 

 plants are and how they live is fundamental to any other 

 study of plants. 



