CHAPTER THREE 



THE PLANT AND ITS ENVIRONMENT 



The seasonal changes in plants and landscapes are so marked 

 that they have always attracted attention. Numerous expla- 

 nations as to why and how these changes are produced have been 

 given. You yourself have probably accounted for the opening of 

 buds in the spring, the blooming of certain flowers during certain 

 seasons, the autumn colorations, and the fall of leaves as the 

 effects of temperature, hght, and moisture conditions. 



Any one who travels extensively will also be impressed by the 

 striking changes in the vegetation as he passes from one region 

 to another. These differences, too, are to be accounted for by 

 the differences in the conditions that surround the plants ; the 

 various types of forests, grasslands, and deserts are the results 

 of climates and soils. Even locally one notices how different 

 the plants are that grow in ponds and swamps, or on cliffs, from 

 those that occur in valley bottoms and on gentle slopes. The 

 plants differ not only in kind, but in size, form, and structure. 

 The plant is profoundly affected by its environment. 



So firmly estabHshed is this fact in our minds that when atten- 

 tion is directed to a familiar plant we at once call to mind the 

 situation in which it grows and perhaps some of the conditions 

 surrounding it. 



Definition of environment. By the environment of a plant is 

 meant the complex of all those influences outside the plant which 

 directly or indirectly ajffect its physiological processes, its structures, 

 and its development and propagation. These influences are 

 numerous and are usually spoken of as environmental factors. 

 The factors of the environment include the physical and chemical 

 properties of the soil and the air surrounding the plant ; also 

 light, gravity, and the influence of other plants and of animals 

 (Fig. 4). 



