D. R. HOAGLAND 



to the study of plant respiration. Goddard, for example, considered 

 the role of the cytochrome system (4). It appears that this system 

 is in fact active in some plant tissues, but not in all. Thus, cytochrome 

 oxidase activity w^as demonstrated in the embryos and roots of certain 

 species of plants, also in immature, but not in adult, leaves. A report 

 is made of the successful isolation of cytochrome G from wheat germ. 

 Wheat cytochrome G has the same absorption spectrum as heart cyto- 

 chrome G. Its reduced form is oxidized by heart or wheat cytochrome 

 oxidase. Succinic dehydrogenase was found to be present in wheat 

 germ in small amounts. 



W. O. James and his associates (10) have undertaken a series 

 of investigations on the enzyme systems extracted from the sap of the 

 barley plant. Here, an ascorbic acid system appeared to be active in 

 normal aerobic respiration. This oxidation system is thought to be 

 characteristic of higher plants. The degradation of sugars, however, 

 seems to proceed by way of well-known reactions of phosphorylation 

 and hydrogen transfer, as described for other kinds of tissue. Various 

 plant storage tissues have been selected by a considerable number of 

 workers as suitable material for the study of respiratory processes. 

 The effects of respiratory inhibitors on these and other plant tissues 

 have also received much attention. 



A comprehensive survey of the literature of plant respiration 

 from the point of view of modern concepts is greatly to be desired, but 

 these examples may perhaps serve to illustrate the point that enzyme 

 chemists can find broad opportunities in the higher plants. This ma- 

 terial provides an important field of research in which the number of 

 workers is inadequate to cope effectively with the many and formidable 

 problems presented. It is reasonable to suppose that a sufficiently in- 

 tensive effort directed at plant research might be calculated to advance 

 the subject of respiratory systems in general, as well as supply much 

 needed basic knowledge for plant nutrition and all its ramifications in 

 agriculture. 



The growth of plants in soil and its dependence on the absorp- 

 tion of inorganic salts or their ions by root cells, with its implications for 

 soil and plant interrelations and for fertilizer practices, brings into the 

 foreground the phenomenon of solute absorption and translocation by 

 living cells — compare the review by Hoagland (9). While these 

 phenomena are of general significance to the study of physiological 



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