1915] SPOEHR—RESPIRATORY ACTIVITY a7. 
rubber stopper. When the amount of carbon dioxide is large, it 
is, of course, advisable to use 0.5 normal solution. The tube was 
then ready for use by turning P; and P,. The error caused by the 
amount of carbon dioxide of the air in the large bulb was found to 
be negligible for these experiments. While one tube was in use, 
the other could be charged. After having drawn the air through 
one tube for the required length of time, the other was inserted into 
the system, and the barium hydroxide solution from the first plus 
the precipitated barium carbonate poured into a narrow bottle, 
well stoppered, and the barium carbonate allowed to settle for 24 
hours; 25cc. of the clear supernatant solution was then titrated 
with o.1 normal hydrochloric acid. From the difference between 
the amount of acid required for the used barium hydroxide solu- 
tion and the original solution, the amount of carbon dioxide evolved 
.can be very simply calculated. In the figure, O is a small wash 
bottle containing barium hydroxide solution, to detect any escaping 
carbon dioxide beyond the Meyer’s tubes; this was never found to 
take place. The rate of air flow was measured by means of the 
gas meter H. At X connection was made with a Palladin pres- 
sure regulator, and this was attached to an electrically driven 
suction pump. 
The nature of the plant material used for these experiments 
was found to be of greatest importance. Briefly, it is necessary 
that the organisms be actively respiring, and that the gaseous 
exchange with the atmosphere be not too difficult. For.instance, 
potato tubers evolve carbon dioxide so slowly that even with a 
large quantity the differences between day and night are exceedingly 
slight. There must also be a sufficient supply of carbohydrate 
food material, for it was found that as soon as the carbohydrates 
were exhausted, the nature of the carbon dioxide evolution 
changed greatly."? The difficulty with wheat seedlings is, of course, 
that the relatively rapid rise and fall of the rate of carbon 
dioxide evolution makes a comparison between day and night 
% Compare DEeLEANO, N. T., Untersuchungen vee den Atmungsstoffwechsel 
abgeschnittener Blatter. Jahrb. Wiss. Bot. 51:541-593- 1912. He found that only 
after the exhaustion of the carbohydrates was there any aes of protoplasmic 
disturbance. 
