296 PHYSIOLOGY 



physics. In certain directions present knowledge is almost or quite 

 sufficient to permit the framing of physical and chemical explanations. 

 In others the data of chemistry and physics are not yet adequate for this; 

 and in still others it seems now quite improbable that the phenomena can 

 ever be analyzed in terms of matter and force. It must not be forgotten, 

 however, that this is the direction of all recent advances, and that what 

 is hopelessly obscure often becomes beautifully clear as some new van- 

 tage point widens the view. 



In its broadest sense, then, plant physiology includes the study of 

 the behavior of plants of all sorts, and of all the ways in which this is 

 affected by external agents of every sort. On the one hand it overlaps 

 morphology, and on the other it includes a large part of ecology. In 

 this book, however, it is restricted in the main to a consideration of the 

 behavior of the larger plants, especially seed plants, though in certain 

 cases reference is made to others. In this part no section on reproduc- 

 tion will be found. That topic is relegated to Morphology (Part I), 

 since the purely physiological processes are relatively simple, so far as 

 known, and very much alike, whereas the reproductive organs are very 

 different in different groups of plants and are most significant for their 

 morphology. For convenience, also, the effect of external agents on 

 plants is treated so as to develop and illustrate general principles, 

 whereas the more extended account of specific cases will be found in 

 Part III, on Ecology. 



