1915] 



MERRILL ELECTROLYTIC DETERMINATION OF EXOSMOSIS 523 



at which time the plants were discarded and a fresh lot of 

 pea seedlings substituted. 



The average reading (value of #) of the water for the 4 

 untreated controls at the beginning was 14.6 on the Wheat- 

 stone bridge, and with the same resistance in the box (9,110 

 ohms) it was 12.6 after 5 days. For the 4 cultures treated 

 with illuminating gas (2 cultures for 3 hours and 2 cultures 

 for 6 hours, the resultant effect being approximately the same 

 for the two periods of exposure) the average initial reading 

 was 17.0 for a resistance of 9,110 ohms, and at the end of 5 

 days it was 43.7 for a resistance of 1,000 ohms. In this case 

 the increase in terms of specific conductivity was from 

 9.2 X 10- 6 to 317.3 X 10" 6 . 



In the 4 cultures placed in the oven at the temperature desig- 

 nated there was no marked difference as regards variation in 

 conductivity of the medium. The average initial reading was 

 17.2 and at the end (after 5 days) it was 12.4, the resistance 

 in the box being 9,110 ohms in both readings. The rather high 

 initial readings in the above cases are due to the fact that it 

 was some hours after the roots were placed in the water be- 

 fore the readings were taken. In later work it was found to 

 be advantageous to have the interval between placing the roots 

 in the water and taking the first reading reduced to exactly 

 one-half hour in order to obtain comparative data on the 

 initial rate of exosmosis under different conditions. 



We have, of course, no indication from the above regarding 

 the exosmosis or conductivity curve during the 5-day interval. 

 Subsequent work shows that it is very probable that the curve 

 rose considerably in the case of the untreated and the oven- 

 treated cultures and then fell, at the end of 5 days, to a posi- 

 tion lower than that of the initial reading, due to the absorp- 

 tion being greater than the excretion after the first 2 or 3 

 days. 



Let us turn now to the results obtained with the fresh seed- 

 lings grown in the same water in which the first crop had re- 

 mained for 5 days under the conditions indicated above. After 

 the second crop had been growing in this medium for just 15 

 days the green weight of tops of the 4 cultures in each group 



