PART I 

 ANATOMY AND PHYSIOLOGY 



I. MEANING OF THE TERMS 



A. Plant physiology is that branch of botany which deals 

 with the vital activities of plants. But physiological 

 processes or functions are carried on by various parts 

 of the plant, and these parts all have their own char- 

 acteristic structure. In order to understand the proc- 

 esses we must know the internal as well as the 

 external structure of the parts concerned. This knowl- 

 edge requires dissection, and this phase of the science 

 is, therefore, called anatomy. Microscopic anatomy is 

 called histology. Just as the processes cannot be 

 intelligently considered apart from the structures 

 involved, so, also, the study of anatomy apart from 

 physiology is meaningless. 



B. In the lowest (i.e., most simply organized) plants all 

 functions, both nutritive and reproductive, are per- 

 formed by every structural unit or cell; but in more 

 highly organized plants there are special parts or 

 organs for the performance of each function; for ex- 

 ample, roots to take in moisture, flowers to form seed. 

 In other words, in the higher plants there is a division 

 of physiological labor, or, as it is sometimes called, a 

 physiological division of labor. While not entirely 

 wanting, the division of physiological labor is less 

 marked in the lowest plants. 



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