K.— BOTANY 231 



by respiration, but how the transfer of the energy is brought about is as 

 obscure as in the case of salt accumulation. 



Thirty years ago, when the importance of the principles of chemical 

 dynamics in life processes was coming to be fully realised, it looked as if 

 the solution of many of the problems of plant physiology in terms of 

 physical chemistry was fairly imminent. But with the application of 

 these principles to our investigations into living processes we find that in 

 every one of them the protoplasm introduces a factor which renders 

 these processes not readily explicable in this way. Clearly we must seek 

 an explanation in the apparent divergence of vital processes from physical 

 or chemical laws in the constitution of the protoplasmic system, and hence 

 a fuller analysis of this system now appears to be a requisite for further 

 advance in our understanding of physiological processes in general. 

 There is at present no reason to suppose that with further advance in 

 knowledge of the protoplasmic system we shall not ultimately be able to 

 explain physiological processes in physico-chemical terms, and I would 

 re-affirm what F. F. Blackman emphasised in his Presidential Address 

 to this Section thirty years ago, namely, 'the inevitableness of physical- 

 chemical principles in the cell.' 



It is scarcely necessary to emphasise how the principles of general cell 

 physiology must be of fundamental importance in plant metabolism, for 

 inasmuch as this depends on the activity of specialised cells and tissues, 

 these, wherever they are alive, must also exhibit the normal features 

 characteristic of protoplasmic activity. The process of photosynthesis 

 involves the absorption of substances by the assimilating cells, and, like 

 those more general cell processes we have considered, depends on the 

 protoplasm in some way not clearly understood, although there is a 

 probability that at least an enzyme is concerned. The passage of the 

 products of photosynthesis from the assimilating cells to the phloem must 

 take place according to the laws governing the movement of dissolved 

 substances into and out of living cells in general. The importance of 

 general cell physiology to absorption by roots is obvious, and here it may 

 be pointed out how the relatively rapid absorption of nutrient salts from 

 soils in which the soil solution is known to be very dilute, is explained by 

 the relationship between concentration and rate of absorption of solutes : 

 the diluter the solution the more rapid the uptake of solute in relation to 

 the concentration. Other physiological problems such as winter hardiness 

 of plants and the effects of extreme conditions in general are also problems 

 of general cell physiology. But in spheres of botanical science outside 

 the range of pure physiology the general physiology of the cell is just as 

 important. This applies in particular to ecology. This study, in so far 

 as its aim is the determination of the relationship of plants to their environ- 

 ment, is indeed nothing else than physiology, a fact which was clearly 

 recognised by Clements more than thirty years ago. Of the two groups 

 of factors which determine the distribution of vegetation, the climatic 

 and edaphic, the mode of action of the latter in particular can only be 

 studied with any hope of success by those with an adequately deep know- 

 ledge and appreciation of cell physiology. It does not need a knowledge 

 of physiology, it is true, to determine plant distribution, but such 



