Hoagland — 96 — Plant Nutrition 



for accelerated movement of salt to the upper part 

 of the plant. Radioactive bromide served as a test 

 element. The suppression of movement of bromide 

 to the upper part of the cucurbit plant was complete 

 for a period of an hour or more. Other experiments 

 on cotton plants with non-radioactive bromide gave 

 similar general results. In the sunflower plant the 

 distribution of bromide between the upper and lower 

 parts of the shoot was definitely influenced by the 

 humidity of the atmosphere, as far as the leaves were 

 concerned. In this instance not much difference was 

 noted in the bromide content of the stem under the 

 two humidity conditions. 



But the question cannot rest here. A plant in a 

 humid atmosphere, even in the light, may be affected 

 in other ways than by changes in the rate of loss of 

 water as has already been indicated by one of the 

 experiments with barley plants. Also, the picture 

 would be incomplete without a reference to the rela- 

 tive accumulation of inorganic solutes by leaves, stems, 

 and other aerial organs. Here, as in the roots, active 

 uptake of solutes by living cells, under the influence 

 of metabolism, assumes great importance. Various 

 factors determine the capacity of the foliar cells to 

 accumulate and to retain solutes. They are essentially 

 the same factors that must be taken into account in 

 explaining salt accumulation by roots. (Compare 

 earlier general statement by Steward, 1935). Not 

 only respiratory activity and associated processes, in- 

 cluding growth, are involved, but also the salt status 

 of the tissue at a given time ; that is, the amount of 

 salt already accumulated in relation to total capacity 

 for accumulation. In experiments of this type low 

 salt tissues of the shoot may be higher in sugar than 

 high salt tissues, as was observed in the experiments 

 on excised roots. In using the term salt in this con- 

 nection the supply of nitrogen may be of special im- 

 portance. 



