PLANT PHYSIOLOGY AND AGRICULTURAL SCIENCES 3 



tools of physics and chemistry in experimental work on plants, and to the 

 interpretation of plant processes in terms of these two sciences. This has led 

 to notable progress in our understanding of the physiology of plants and has 

 permitted the analjsis and expression of many physiological relations in quan- 

 titative terms. 



A knowledge of certain fundamental principles of physics and chemistry 

 is therefore essential to the understanding of physiological processes. For this 

 reason several of the earlier and parts of some of the later chapters in this 

 book are devoted to a brief exposition of those underlying principles 

 of the physical sciences with which a student of plant physiologj' should be 

 familiar. 



The Relation of Plant Physiology to the Agricultural Sciences. — 

 Green plants are not only the ultimate source of all food but supply the raw 

 materials for many of our basic industries. With the rise of modern industrial 

 civilization both the quantities and kinds of plant products which we utilize 

 have increased rather than decreased. In addition to foods some of the more 

 important raw products obtained from plants are wood, textile fibers, pulp, 

 rubber, vegetable oils, gums and drugs. Even most of the so-called "synthetic 

 products" of the chemist are not synthetic in the sense that they have been built 

 up from simple inorganic compounds, but only insofar as they represent modifi- 

 cations of naturally occurring plant products. 



An industrial civilization not only requires a wide variety of plant products 

 but insists that these products meet certain standards of quality. The success- 

 ful cultivation of plants has, therefore, become a highly skilled occupation, and 

 the agricultural sciences are rapidly becoming a domain of the specialist. 

 Success in controlling the activities of living plants can not be achieved without 

 some understanding of the processes which occur within them, and of the 

 effects of environmental conditions upon these processes. The problems of the 

 forester, the fruit grower, the cotton planter, the floriculturist, the grain 

 farmer, and of all others who cultivate plants differ in detail, yet they all have 

 a fundamental similarity in requiring an application of the principles of plant 

 physiology for their solution. 



Fundamental investigations in plant physiology have contributed in many 

 ways to improved methods of propagating, cultivating and harvesting eco- 

 nomically important plants, and to methods of handling and storing many plant 

 products. Furthermore, control of the fungous diseases and insect predators 

 of plants often requires application of the principles of plant physiology'. 

 Much of the investigational work carried on by scientific agronomists, horti- 

 culturists, floriculturists, and foresters actually lies in the field of pure or 

 applied plant physiolog}^, although often it is not formally classed as such. 



