1915] 



MERRILL ELECTROLYTIC DETERMINATION OF EXOSMOSIS 521 



full nutrient medium, after which they were transferred to dis- 

 tilled water. In all instances, however, the roots were care- 



fully rinsed before being placed in the water. 1 



To determine if any impurities had contaminated the dis- 

 tilled water in the cultures treated with ice, the distilled water 

 in No. 4 was renewed after the operation. The resulting crop, 

 however, was practically the same in cultures 3 and 4 and hence 

 it may be considered that no plant food had entered from the 

 ice. The distilled water was renewed in No. 10 a few hours 

 after the treatment. The result of so doing was to discard the 

 plant foods already excreted during, and immediately after, 

 the treatment. This fact was evident from the better growth 

 of the plants in No. 9 as compared with those in No. 10. Later 

 work also showed that exosmosis caused by treatment with 

 illuminating gas and other agents is comparatively rapid and 

 immediate. 



After the treatment the plants remained in the distilled 

 water for 5-6 days, after which they were discarded. The dis- 

 tilled water level was then raised to the original height by 

 adding fresh distilled water, and into this medium fresh Can- 

 ada field pea seedlings were placed and the resulting growth 

 determined. Cultures Nos. 17-24 are given in table i for 

 comparison. After pea seedlings had been grown for 21 days 

 in the unrenewed distilled water of cultures 17-20, the original 

 plants were discarded and fresh seedlings of peas and horse 

 beans were placed in the same distilled water. For compari- 

 son, cultures of these plants (Nos. 21-24) were set up at the 

 same time in fresh distilled water. 



Returning now to the effects of the treatments on the plants 

 and noting the results given in table i, we see marked differ- 

 ences evident. Neither the ice nor the inoculation with Asco- 

 chyta Pisi 2 produced any effect either on the plants or on the 

 excretions from their roots, and hence these cultures are sim- 



1 The usual method of rinsing throughout this work was as follows: The 

 solution to be discarded was thrown out, the tumbler filled twice with once-distilled 

 water (the roots replaced and the whole thoroughly shaken each time), and then 

 distilled water (redistilled) was added, the roots replaced, and the readings taken. 



* Cultures of Ascochyta Pisi were kindly supplied the writer by Dr. R. E. 

 Vaughan. 



