CHAPTER IX 

 THE PLANT AND ITS ENVIRONMENT 



The form which a plant assumes and the activities which it 

 carries on are due to the combined effect of two major causes. 

 These are, first, the inherent characteristics of the plant itself, 

 determined by the specific constitution of its protoplasm and 

 transmitted from one generation to another by heredity; and, 

 second, the surroundings or environment in which the plant 

 lives. Plants are so diverse and environments so varied that the 

 relations which exist between the one and the other are many and 

 complicated. A study of these relations forms the subject matter 

 of the science of Plant Ecology, some of the problems of which we 

 shall discuss briefly in this chapter. 



It is evident that even for the same plant, growing in the same 

 spot, the conditions of light, temperature, moisture and various 

 soil factors may change radically. Between two plants in differ- 

 ent places, environmental differences may be even more marked. 

 We have already learned enough of plant physiology to know 

 that these various external factors may vitally affect the way in 

 which the plant functions, and it is therefore evident that if a 

 plant is to thrive and maintain itself, it must be able to modify 

 its form and activities to meet this ever-changing environment 

 successfully. One of the most remarkable facts of biology is 

 that organisms do possess, in greater or less degree, this character- 

 istic of advantageous regulation of structure and function in 

 conformity to the changing external world. As to what are the 

 causes of these regulations there is much difference of opinion 

 and no certain knowledge. In describing plant activities, most of 

 which contribute so obviously to the welfare of the individual, 

 we continually find ourselves using terms which imply purpose or 

 effort. It is indeed very difficult to describe the facts of form and 

 function in simple language without tacitly assuming that there 

 is within the plant something which directs and regulates its life 

 so that it will tend to do whatever is to its own best advantage. 

 Such an assumption is, of course, quite contrary to the modern 



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