602 Physiologie. 



and reactions was, of course, a splendid advance, the early deve- 

 lopment and extension of which we owe largely to our Veteran phy- 

 siologist Professor Pfeffer of Leipzig. Great as is the Service it 

 has rendered to many departments of botany, yet in one direction, 

 I think, it has overfiowed its legitimate bounds and swamped the 

 development of the physical-chemical concepts which I shall indicate 

 later on. 



The address then proceeds to a short exposition of the four 

 quantitative principles which govern every Single chemical reaction 

 which are respectively concerned with 1. the nature of the reaction 

 2. the amount of reacting substances 3. the temperature and 4 the 

 influence of catalysts. 



The metabolism of the Plant considered as a Catalytic Reaction. 

 Plants of all types throughout their active life are continually gro- 

 wing by the excess of anabolism over katabolism; in the congeries 

 of their metabolic processes metabolism may be regarded crudely 

 as a collection of slow chemical reactions and should conform to 

 the laws of chemical mechanics outlined in the previous section. 



Now this complex reaction of metabolism only takes place in the 

 presence of protoplasm , and a small amount of protoplasm is capable 

 of carrying out a considerable amount of metabolic change, remai- 

 ning itself undestroyed. We are thus led to formulate the idea that 

 metabolism is essentially a catalytic process. In support of this we 

 know that many of the inherent parts of the protoplasmic complex 

 are catalytic enzymes, for these can be separated out of the proto- 

 plasm, often simply by high mechanical pressure. 



If metabolism is a complex of up-grade and down-grade changes 

 catalysed by protoplasm we must expect the amount of metabolism 

 to obey the law of mass and to be proportional to the masses of 

 substances entering into the reaction. The case when any one essen- 

 tial element is a limiting factor is a comparatively simple one. 

 When all are in excess, then the amount of the catalyst pre- 

 sent becomes in its turn the limiting factor. Transferring this point 

 of view to the growing plant, we expect to find the limited mass of 

 protoplasm and its constituent catalysts setting a limit to the rate 

 of metabolic change in this extreme case. 



These two cases exemplifying the law of mass were illustrated 

 by the work of Palladine on the relation of seedling respiration 

 to active nitrogen, and the investigations of Blackman and Mat- 

 thaei on the respiration of leaves. 



The quantitative aspects of the growth of plants, exemplifying 

 the totality of metabolic reactions, also furnishes illustrations of the 

 action of the law of mass. The increase of the amount of catalytic 

 protoplasm by its own catalytic activity is a phenomenon which the 

 chemist would classify as a case of 'autocatalysis'. 



The free manifestation of an autocatalytic rate, of growth will 

 result in continually increasing increments of growth in successive 

 equal intervals of time, graphically representable by a logarithmic 

 curve of increasing mass. The growth of such diverse plants as 

 bacteria and the maize plants investigated by Mlle Stefanowska 

 illustrate this clearly. 



It is suggested that where small traces of added substances like 

 metallic salts, accelerate growth considerably the ingested substance 

 really plays the part of an added catalist to the protoplasm and is 

 not rightly to be considered as a 'chemical Stimulus'. 



Ja villi er's recent quantitative study of the effect of various 



