K.— BOTANY 223 



While a synthesis of what may be called protoplasmic proteins and other 

 substances is taking place in the growth centres, this synthesis is much 

 less than the breakdown of protein reserves, and it would therefore 

 appear that in such material there is a source of energy available apart 

 from that provided by the breakdown of carbohydrate. Before we can 

 hope to present a picture of the relations between respiration and vital 

 syntheses in germinating seeds, and perhaps in all other material as well, 

 it seems to me that we need not only many more data regarding respira- 

 tion rates under both aerobic and anaerobic conditions throughout the 

 whole germination period, but also a detailed biochemical analysis of the 

 carbohydrate and various nitrogenous materials present in the seedlings. 

 So expressed, this may sound and look a simple enough matter, but 

 actually, as anyone who has attempted to tackle such problems knows, it 

 is one that abounds in difficulties. 



As far, then, as the mechanism by which respiration provides the 

 energy for the formation of compounds of higher energy content is 

 concerned, we are still very much in the dark. There is even the possi- 

 bility that we are completely wrong in assuming a connection between 

 aerobic and anaerobic respiration. While there is very strong evidence 

 that anaerobic respiration in plants is often similar to fermentation, in- 

 asmuch as the substrate and the end products are the same, there are so 

 many exceptions, or apparent exceptions, to the production of ethyl 

 alcohol in the correct quantity demanded by the equation for fermenta- 

 tion, that one may well hesitate in accepting this view as of universal 

 applicability. On the other hand, the opinion of Miiller and Lundsgaardh 

 that anaerobic respiration is a process quite distinct from aerobic respi- 

 ration, in which different enzymes function and in which the course 

 of the breakdown is different from the beginning, has found little support 

 from more recent work. The view of anaerobic respiration as the effect 

 of deprivation of oxygen on the normal aerobic process, appears to me 

 by far the more reasonable one. For if the two processes were completely 

 independent we should expect anaerobic respiration to proceed at all 

 times, in both presence or absence of oxygen, or we should have to assume 

 that oxygen inhibits the breakdown of carbohydrate to carbon dioxide 

 and ethyl alcohol. Now the first hypothesis is untenable because it 

 would mean that in air aerobic respiration took place in addition to 

 anaerobic respiration, so that the output of carbon dioxide under such 

 conditions should always be greater than in absence of oxygen, which 

 is not always the case. Nor do the products of anaerobic respiration 

 normally appear in presence of air. On the other hand, the breakdown 

 of carbohydrate to carbon dioxide and alcohol by the enzyme complex 

 zymase does not appear to be inhibited by oxygen. 



While it has generally been assumed that respiration is linked in some 

 unknown way with the synthesis of proteins and other substances, its 

 connection with those other processes, the absorption and excretion of 

 materials which are characteristic of cells, has only come to be appreciated 

 more recently. The absorption and excretion of water and dissolved 

 substances was generally more or less tacitly assumed to be determined 

 by the physical laws of osmosis and diffusion. Water was supposed to 



