Hoagland —128— Plant Nutrition 



be appropriate in this lecture, however, to undertake 

 a controversial discussion. The results of the experi- 

 ments to be considered may incidentally have a bear- 

 ing on the theory outlined, but the main purpose is 

 more general. 



More sugar usually disappears from excised roots 

 when potassium salts are absorbed than when absorp- 

 tion occurs from calcium salts and almost always res- 

 piration is accelerated more by potassium salts than 

 by calcium salts.* Sugar concentration in the roots 

 does not, within wide limits, determine directly the 

 rate of respiration. One of the problems that awaits 

 further investigation is concerned with the fate of 

 sugar during root respiration and salt accumulation. 

 Much more sugar may disappear from the roots than 

 is accounted for by the CO2 evolved. It is probable 

 that part of the sugar is converted into polysaccharide 

 form, but the direct evidence for this is not at present 

 available. Appreciable amounts of starch are not 

 found in these barley roots but another hexosan has 

 been isolated. 



Salt Absorption and Organic Acids : — A question 

 of first importance in the study of the inorganic nu- 

 trition of plants in relation to biochemical processes 

 is that of the effects of salt absorption on the organic 

 acid system of the plant cell. By organic acids in this 

 connection is meant the ether-soluble, non-volatile or- 

 ganic acids, particularly oxalic, succinic, malic and 

 citric acids, and no doubt others entering into cycles 

 of organic acid transformations. 



Organic acids of this type are of great significance 

 in the metabolism of plant cells and some of them 

 have as one function a role in buffer systems of the 



*In the absorption of ions from calcium solutions but little 

 calcium is absorbed. With respect to absorption of ions by 

 roots from calcium bromide solutions, the equivalent of bromide 

 removed from solution exceed greatly those of calcium but more 

 bromide is removed from a potassium salt than from a calcium 

 salt. 



