K.— BOTANY 229 



leading to poor oxygen supply may be related not only to oxygen con- 

 centration but also to accumulation of carbon dioxide and other products 

 of anaerobic respiration. Hoagland's observations on the absorption 

 of potassium bromide by cells of Nitella may, perhaps, be of significance 

 in regard to the part played by oxygen in salt absorption. He found that 

 absorption of bromide only took place if the cells were exposed to light, 

 or if they have been previously exposed to adequate illumination. If for 

 some time previously they had been growing in weak light no accumulation 

 of the salt or its ions took place. From a consideration of all the data it 

 seems to me that the following conclusion can be drawn regarding the 

 relationship of respiration to the absorption of salts by plant cells, namely, 

 that accumulation of salt depends on the vitality of the cells and that the 

 maintenance of this vitality depends, as has been long recognised, on the 

 presence of oxygen, either because aerobic respiration or some other 

 process requiring oxygen is essential for this maintenance of vitality, 

 or because in the absence of oxygen the accumulation of carbon dioxide 

 and other products of anaerobic respiration adversely affects the function- 

 ing of the protoplasm. This dependence of absorption of salts on the 

 vitality or healthiness of the tissue was clearly shown by my experiments 

 of 1927 and the later ones of Steward in which stress was laid on the effect 

 of aeration of the tissues. I think Hoagland's observations fall into line 

 with these. Nitella kept for some time in low light is probably somewhat 

 unhealthy, just as is tissue that is deprived of an adequate supply of 

 oxygen. In other words, most of the work published on the relationship 

 between respiration and salt accumulation does no more than show that 

 this accumulation is a vital process, depending on the normal functioning 

 of the protoplasm. Any general relationship between respiration and salt 

 accumulation, as regards the linkage of reactions involved or the transfer 

 of the energy required for the entry of a salt against its own diffusion 

 gradient, may thus be very indirect. 



This view of the necessity of oxygen for salt accumulation does not rule 

 out the possibilities of adsorption, chemical combination and ionic inter- 

 change as playing a part in salt absorption, and indeed, my experiments 

 of 1927 and those of Briggs and Petrie of 1931, to which I have earlier 

 referred, are most readily explicable in terms of ionic interchange. Apart 

 from the more obvious physico-chemical relationships already mentioned, 

 what is called decline in vitality, health or activity is associated with 

 changes in the protoplasm, which may involve changes in the state of 

 aggregation of the protoplasmic colloids and in the distribution of their 

 various constituents, which will profoundly alter their capacity for ad- 

 sorption or chemical combination and the nature of ionic exchanges. 

 I am certain that in the present state of our knowledge there is no justi- 

 fication for putting aside any of these processes as possibly playing a part 

 in determining the salt relations of cells. What is required for the clari- 

 fication of the problem I have emphasised for many years, namely, the 

 accumulation of experimental data regarding these relations, and it should 

 help greatly if data are obtained for different kinds of cells and with 

 different kinds of solutes. With the development of both chemical and 

 physical methods for the measurement of small quantities, such data can 



