204 STUDIES ON RESPIRATION. IV 



were determined, the periods were usually comparatively long, 1 or 2 

 hours, and therefore the complete series of changes in the rate of 

 respiration could not be followed. 



The material chosen for these experiments was wheat, as repre- 

 senting the flowering plants. The anesthetic used was ether in 7.3 

 and 3.65 per cent solutions, by volume. 



Wheat seeds were soaked for 12 hours, during which time the 

 process of germination enters upon its first stages. Seeds were 

 selected which were as nearly alike as possible; twenty-five were 

 placed in a Pyrex tube with 10 cc. of water containing five drops of the 

 indicator, 0.01 per cent phenolsulfonephthalein. The tube was 

 closed so that all air was excluded and the seeds themselves acted 

 as a stirrer. 



It was found convenient to allow the seeds to give off enough CO2 

 to change the solution from a pH value of 7.78 to a pH value of 7.36. 

 This range of color change was arbitrarily selected as definite and 

 easy to read, and formed the standard for all the experiments. Tap 

 water which had been boiled to drive off the CO2 sufficiently to give 

 a pH value shghtly higher than 7.78 was used in all cases. At the 

 end of each period the liquid was poured out and fresh tap water 

 was added. A normal rate of respiration was first estabHshed by 

 repeated determinations,^ then the reagent was added and the rate 

 again determined. All results were expressed in per cent of the nor- 

 mal rate, which was called 100 per cent. 



In these experiments the colors were matched with the aid of a 

 "Dayhght" lamp, which gave a constant source of light. The ex- 

 periments were made at room temperature, about 18-20°C.^'' 



The stock solution of ether was a saturated solution in tap water 

 (containing the indicator of the standard concentration). In order 

 to have the solution of the right pH value at the start (pH 7.78), 

 two bottles of 7.3 per cent ether were kept on hand;^^ these had 

 different pH values and by mixing, the desired value was attained. 



* This was taken as the reciprocal of the time required to change the pH value 

 from 7.78 to 7.36. 



10 For other details of technique see Paper I (Osterhout, W. J. V., /. Gen. 

 Physiol., 1918, i, 171. 



" Glass stoppered bottles of Kavalier glass (which does not give off sufficient 

 alkali to interfere with the experiment) were employed for this purpose. 



