PHYSIOLOGY OF PLANTS 



VOLUME II. GROWTH, REPRODUCTION, AND MAINTENANCE 



CHAPTER I 



GROWTH 

 SECTION I. General. 



METABOLISM necessarily accompanies all forms of vital activity, 

 and hence also the growth and growth-movements occurring during the 

 progress of development (cf. Vol. I, Chap. I). The character of the latter 

 is determined by the inherited properties of the embryonic organism, 

 and the formative activity is directed along a predetermined path leading 

 ultimately to the production of a specifically distinct individual. It is 

 not however possible to deduce the actual results as the necessary con- 

 sequence of the given dispositions, that is from the interaction of various 

 forms of energy with materials of definite structure. To render such 

 deductive treatment possible still remains the ideal of Physiology, and only 

 when this ideal has been attained shall we be able to obtain a com- 

 prehensive view of the interacting factors at work in the living organism. 



In the present state of our knowledge, however, it will perhaps be 

 best to treat the subject more empirically. Hence, neglecting special 

 morphological peculiarities, we shall first deal with the character and 

 progress of growth under normal and constant external conditions, and 

 shall then discuss the mechanics of growth (Chap. II). The influence 

 of the external (Chap. VI) and internal (Chap. VII) conditions upon growth 

 will be treated as separate subjects. 



The most difficult problems are those concerned with the autonomic 

 direction and regulation of growth, and indeed our knowledge is here very 

 fragmentary, for we are dealing with phenomena of extremely complex 

 origin. Among the co-operating factors are the numerous and varied 

 stimulating and mechanical interactions between different organs, between 

 different cells, and between the different parts of the same protoplast. 

 It is by interaction of this kind that the partial functions are correlated, 

 and the character of the combination producing harmonious co-operation 

 may differ according to the end in view (cf. Vol. I, Sect. 4). 



Every form of growth is an automorphic change, that is, it is produced 

 by the plant's own activity. The same is also the case when the external 

 conditions modify the character or rapidity of the formative changes. 



PFEFFER. II B 



