8 INTRODUCTORY 



the aid of a very high-power microscope, while others are of 

 very great size. Their processes. x>i life vary greatly with the 

 conditions under which they live. We very generally consider 

 the higher plants of the greatest importance to man, but a knowl- 

 edge of botany lea,ds us to an appreciation of the very great im- 

 portance of the apparently insignificant forms of plant life. 

 Some of these extremely small plants are of great importance in 

 certain industries, while others are the causes of diseases of 

 higher plants and of animals. We will give the greater part 

 of our attention to the higher forms of plant life, to the flow- 

 ering plants. 



These higher plants consist of three parts, the roots, stems 

 and leaves; the other parts, such as flowers and fruits, are spe- 

 cializations of some one or more of these primary parts. The 

 roots serve for anchorage or holdfasts, for the securing of water 

 aiid certain food materials and for storage; the stems connect 

 the roots and the leaves and serve some other functions; the 

 leaves absorb the energy of sunlight and serve for transpiration, 

 photosynthesis and other functions. The flowers and fruits are 

 leaves which are specialized for reproduction. The functions of 

 these organs will be explained more fully in later chapters. 



These higher plants grow from seeds, eventually producing 

 another generation of flowers and seeds. Some plants complete 

 this cycle in one season and are known as annuals; others com- 

 plete their cycle in two years and are known as biennials; while 

 others live for many years, producing seeds year after year, and 

 are known as perennials. Some flowering plants have partly or 

 completjely lost the power of rroducing seeds and reproduce vege- 

 tatively (pages 101-107). 



The plant is made up of many kinds of cells which are micro- 



