DILUTE SOLUTIOIS^S AS STIMULANTS. 43 



sthnulating effect upon growth, as compared with that hi the rtistillecl 

 water control during a corresponding period. This was shown to be tlie case 

 for salts of calcium, both the chlorid and the sulphate acting as stimuli. 



These investigators found decisive evidence of such stimuhitin<i- 

 action with both the carbonate and the bicarbonate of sodium. 

 Sodium sulphate and sodium chlorid gave purely negative results. 

 Verv marked results of this kind were observed by Cameron and 

 Breazeale when working with acids. Hydrochloric, sulphuric, and 

 nitric acids in concentrations but little beloAv the toxic limit produced 

 enormous stimulation, especially with Avheat. 



Copeland" shows that zinc and copper in water cultures accelerate 

 <:-r(jwth when the solutions are not nnich more dilute than those that 

 are distinctly toxic. Similar observations have been made by many 

 earlier investigators. 



In the experiments with wheat all the salts were found to stimu- 

 late growth except sodium chlorid and sodium carbonate, which were 

 indifferent at the lowest concentration used. It is not unlikely, 

 however, that if the proper dilution of the carbonate were employed 

 it would be found to act as a stimulus with wheats just as it did with 

 lupines. In fact, it was found that the same concentration of certain 

 salts which was decidedly toxic for some varieties of wheat will 

 act as a stimulant to another variety. Especially is this true of the 

 chlorid and sulphate of magnesium. In a 0.005 solution of each of 

 these salts the elongation of the roots of Turkey Avheat was equal to 

 that in the control of hydrant water during the period of twenty- 

 four hours. The toxic limits for this variety are 0.0075 normal for 

 the chlorid and 0.01 normal for the sulphate. As will be seen, two- 

 thirds and one-half the concentration of the toxic limit, respectively, 

 not only were not toxic but actually acted as a stimulating influence. 

 There is a possibility, in view of these results, that dilutions not very 

 much below the toxic limit are more likely to have a stimidating 

 effect than are much more dilute solutions. This, however, is not 

 a question to be settled at this time. l)ut will require to determine it 

 a series of special experiments. 



A 0.015 normal solution of sodium sulphate caused an elongation 

 about one and one-half times as great as that in hydrant water. The 

 same dilution of sodium chlorid gave results somewhat less striking, 

 but the elongation was well above the average of that in the hydrant- 

 water checks. 



As before stated, it would seem that instead of being injurious, 

 dilute solutions of these salts might be decidedly advantageous, yet 

 if they cause an unnatural growth their presence must be considered 

 as detrimental rather than beneficial. Copeland calls attention to 



n Chemical Stimulation and the Evolution of Carbon- Dioxide. Bot. Gaz., 



35: 81 -as (UK):;). 



