47 



be regarded as generic properties of protoplasm. No less important, 

 as Loeb\s work A\ith animals lias eonelusiveh' shown, will be the com- 

 parative study of different organs and functions and stages of growth 

 in the same plant, as to their different reactions to the same ions and 

 combinations of ions. 



From the point of view of agriculture the ion-j^roteid theory will 

 doubtless throw light upon much that is now obscure and even para- 

 doxical in the relation between the plant and the soluble components 

 of the soil. Nothing is more certain, in the light of such observations 

 as are recorded in this paper, than the inadequacy of soil pliysics and 

 soil chemistry alone to explain mau}^ d,etails of this relation. The 

 chemistry of protoplasm and its proteid compounds must surely be 

 taken into account before we may hope to get to the bottom of the 

 subject. 



STIMULATIXG EFFECT OF DILUTE SOLUTIONS. 



As an incident of these investigations it was demonstrated that in 

 the case of certain salts, when plant roots are exposed to pure solu- 

 tions which are much too dilute to produce any toxic effect, there 

 occurred a decidedh' stimulating effect upon growth, as compared 

 with that in the distilled-water control during a corresponding period. 

 As would be expected, this was shown to be the case for salts of cal- 

 cium, both the chloride and the suli3hate acting as stimuli. Here, 

 however, we have to do with salts which contain valuable elements 

 of plant food. 



But a marked stimulating action occurs in pure solutions of sodium 

 carbonate (slight in 0.002 normal, marked in 0.00125 normal and of 

 sodium bicarbonate 0.01 normal). The most pronounced effect was 

 obtained in a 0.00125 normal solution of sodium carbonate, the average 

 elongation of the roots in that solution being one and one-half times 

 as great as in distilled water during the same period. In the case of 

 the two carbonates of sodium it seems necessary to regard the effect as 

 one of chemical stimulus, pure and simple. That this is not due to the 

 sodium ions is evident from the fact that very dilute solutions of other 

 sodium salts (sulphate, chloride) gave purely negative results. It was 

 at first thought that the physiological effects of sodium carbonate 

 (NagCOg) were attributable to the presence of hydroxylions in the solu- 

 tion, since the corrosive, clearing action of more concentrated solutions 

 of this salt is precise!}' similar to that produced by potassium hydrate 

 and sodium hydrate. But toxic, as well as stimulating reactions of 

 exactly the same character were obtained with solutions of the bicar- 

 bonate (NaHCOg), in which a large excess of carbon dioxide was dis- 

 solved, and which gave no reaction with phenolphthaleine, even at the 

 end of the experiment. ^ In this case the consideration of free hydroxyl 



' Solutions of sodium carbonate which were many times too dilute to produce a 

 stimulating effect, yet gave a strong reaction with phenolphthaleine. 



