Tue CARBON DIOXIDE OF THE Sort AIR 335 
different media as is the weight of the plant itself. Hasselbring (1914), 
however, after growing plants under cheesecloth and in the open, stated 
that the mere passage of water thru the plant had no influence on the 
assimilatory activity of the plant, provided the water supply did not 
fall below a certain minimum required to maintain turgor of the cells. 
Stoklasa and Ernest (1909) determined the carbon dioxide given off by 
different plants grown in various nutrient solutions, and obtained the 
results presented in table 5 (appendix, page 358). These figures show 
that there is a definite relationship between the total dry weight of. 
different crops and the carbon dioxide produced. ‘The average of 0.037 
milligram of carbon dioxide to each milligram of dry matter seems to be 
independent of the kind of plant used in the test. 
From the short review given, it would seem that the evidence is in 
favor of the assumption that transpiration is related te life activity of 
plants as indicated by a relationship between the dry matter and the 
water transpired. The work of Stoklasa and Ernest (1909) would point 
to a correlation between the carbon dioxide produced and the dry matter 
in the plant. 
Effect of temperature and atmospheric pressure 
The relationship between the temperature and the atmospheric pressure 
at the time of sampling, and the carbon dioxide in the air of the uncropped 
soil, is shown graphically in figures 50 and 51 for the seasons of 1917 and 
1918, respectively. The temperature at each time of sampling was found 
to be approximately representative of the temperature for the preceding 
twelve-hours period. The pressure also would probably represent the 
average of several hours preceding the sampling. 
On the whole the figures bring out only a few striking facts. High 
temperatures were usually accompanied by a high percentage of carbon 
dioxide, while high atmospheric pressures were usually associated with 
a low carbon-dioxide content. High pressures along with high tem- 
peratures gave fairly high contents of carbon dioxide, indicating that 
temperature has a more marked effect than pressure. When the temper- 
ature and the pressure were medium there appeared to be no relationship 
with the carbon-dioxide content. Very low temperatures were always 
accompanied by alow content of carbon dioxide; but, while a very low 
pressure did not necessarily mean a high carbon-dioxide content, it was 
usually associated with such a condition. 
