1915] SPOEHR—RESPIRATORY ACTIVITY 373 
that drawing air through the barium hydroxide solution would 
evaporate some water, thus make the solution more concentrated, 
and hence give lower values for the longer periods. The following 
blank experiment eliminates this possibility. 
25cc. original Ba(OH). solution= 27. IQcc. 6 I SHC 
25cc. after 3.5 hours =27.05CC. 
25cc. after 16 hours = 26.99CCc. 
That differences in atmospheric pressure might account for 
the daily variation in carbon dioxide evolution also suggested itself. 
The exceedingly slight variations of pressure at Tucson bear no 
possible similarity to the values of respiration. 
“ cc 
Experimental results 
The following is a brief account of a few typical experiments 
carried out during the winter of 1913-1914. The first column in the 
tables gives the number of the carbon dioxide determination; the 
second, the time of day during which it ran; the third, the number 
of hours; the fourth, the rate per hour at which the air was drawn 
over the plants in liters; the fifth, the rate of carbon dioxide 
evolved per hour, expressed in milligrams. In the sixth column 
the weather is roughly indicated: A stands for a perfectly cloudless 
day; B, a few scattered cumulus clouds; C, more clouds than B, 
usually thin cirrus; O, overcast; and R, rain. 
The curves are plotted with the rate of carbon dioxide evolution 
per hour in mg. on the ordinates, the successive determinations 
on the abscissas; the broken lines indicate the day rates, the solid 
lines the night rates. : 
(1) The first experiments (p. 374) were made with small onion 
bulbs (Australian brown) 0.75-1 inch in diameter. In order to 
insure ease of gaseous exchange in the onions, the dry outer layers 
were removed. Previous experiments showed that this operation 
resulted in but a very slight traumatic effect. After 24 hours, 
35 of these small onions were placed in flask R. To prevent drying 
out, the air was drawn over water contained in a bottle inserted 
between the tubes G and the flask R. The experiment ran from 
January 21 to February 2. The results are given in table I and 
fig. 2. Here it can be seen that the differences in carbon dioxide 
