INTRODUCTION 5 



A fifth subject of study is the life-relations of plants. 

 Plants become related effectively to such things outside 

 of themselves as light, water, soil, and other plants, and 

 how this is accomplished is the subject referred to. Plants 

 may be studied as individuals relating themselves to their 

 surroundings, just as a human individual may be studied 

 as he adjusts himself to the conditions of life in a city; or 

 they may be studied in " vegetation masses," such as 

 forests or prairies, just as groups of people in a city may 

 be studied as they adjust themselves to other groups. 

 One great natural vegetation mass is of such practical 

 importance that it has developed the special subject of 

 forestry. 



A sixth subject is known as plant-breeding, and it has 

 become of great scientific and practical importance. It 

 means the growing of plants, generation after generation, 

 under observation and control, and trying to discover the 

 laws of inheritance, which we usually call heredity. This 

 is the great scientific importance of plant-breeding. Its 

 practical importance comes from the fact that the scien- 

 tific work has suggested methods of improving our old plants, 

 producing new ones, and guarding our crops against disease 

 and drought. From the standpoint of our material in- 

 terests nothing can be more important, for it lies at the basis 

 of the world's food supply. 



The six aspects of plants described above do not exhaust 

 the list, but they are conspicuous illustrations of the fact 

 that botany is not a single study, but includes many kinds 

 of study. 



6. Simple and complex plants. Plants differ greatly 

 not only in size, from microscopic forms to huge trees, but 

 also in complexity of structure. Some plants are so simple 

 that all regions of the body are alike, while others are so 

 complex that the body consists of many kinds of structures. 

 Although the structure of simple and complex plants is 

 2 



