228 SECTIONAL ADDRESSES 



but the problem is complex, for the effect of carbon dioxide accumulation 

 in poorly aerated solutions may be a factor, and there is a marked difference 

 in the reaction of different species, for both Free in America and Jorgensen 

 and myself in this country found that buckwheat cultures did not react 

 to differences in the oxygen supply to the roots, while as regards maize, 

 whereas Andrews and Beal found that aeration of the culture solution 

 very greatly increased the yield. Knight found that this was the case with 

 soil cultures, but not with water cultures. Whether this divergence in 

 behaviour is to be related to varietal differences or to some undefined 

 factor in the experiments is not clear. 



More direct evidence of the effect of oxygen on the salt relations of the 

 cells has been obtained in work with storage tissues. In 1927, as a result 

 of observations on the behaviour of such tissues when placed in water 

 either kept still or agitated, I called attention to the importance of respira- 

 tion in regard to the salt relations of the cells. I pointed out the import- 

 ance of maintaining the supply of oxygen to such tissues for the maintenance 

 of their vitality, and that in the absence of an adequate oxygen supply 

 exosmosis of electrolytes took place, leading to the speedy death of the 

 tissues, whereas with maintenance of a supply of oxygen absorption of 

 electrolytes continued, in the case of beetroot, for example, for periods 

 of about three weeks. Towards the end of this time a condition of 

 equilibrium was reached or approached, in which the content of 

 electrolytes in the external liquid was very low. During this period 

 conditions leading to lower oxygen and higher carbon dioxide concentra- 

 tion led to increase in the electrolyte content of the liquid, while addition 

 of fresh oxygen led to a decrease. In similar experiments carried out by 

 Briggs and Petrie in 193 1 in which a continuous stream of air was passed 

 through the liquid, these workers examined the course of respiration along 

 with the changes in electrolyte content of the external solution, and 

 established the fact that there was a general parallelism between the rate 

 of respiration of the tissue and the electrolyte concentration of the external 

 liquid. If the stream of air was replaced by nitrogen the respiration rate 

 increased, and so did the concentration of electrolytes in the solution, 

 while replacement of the nitrogen by air brought back the original dis- 

 tribution of electrolytes between tissue and external liquid. Steward and 

 collaborators have shown that reduction of the oxygen supply to storage 

 tissue of potato, carrot and artichoke below a certain value limits the 

 accumulation of both the ions of potassium bromide by the tissues, while 

 Hoagland and Broyer have obtained a similar result with barley root 

 systems. In attempting to explain this effect of oxygen one must bear in 

 mind that the relationship between respiration and salt accumulation 

 may not be a direct one. The maintenance of an adequate supply of 

 oxygen is necessary to maintain the vitality of the tissue, possibly on 

 account of the deleterious effects of the products of anaerobic respira- 

 tion. Thus the fact that accumulation depends on oxygen supply may be 

 regarded as an expression of the fact that under conditions of partial or 

 complete anaerobiosis the functioning of all or many vital processes 

 dependent on the protoplasm is adversely affected, and along with them 

 that of salt accumulation. From this point of view the effect of conditions 



