386 Dr. F. F. Blackman and Mr. A. M. Smith. [Dec. 19, 
analysed. Its total volume was 27-4 c.c., containing 3°6 c.c. CO2 = 1°5 cc. CO» 
per hour. Therefore the average correction to be applied for the whole 
experiment was taken at 1°3 c.c. CO2 per hour = 000239 germ. CO, 
(taking the weight of 1 cc. CO, at laboratory temperature and pressure as 
0:00184 grm.). 
(8) During the experiment COs is being formed in respiration both in the 
illuminated parts and in the shaded leaves in the background, we. by the 
whole weight of tissue present. Several separate experiments to determine 
the respiration were made at different temperatures, using the same 
procedure as in this experiment except that the bath was darkened. Some 
of these were made on Elodea before feeding up by assimilation, and others 
after several hours’ preliminary assimilation, whereby the respiration is 
increased. The mean of the two values was taken as basis for a correction. 
The measurements of respiration were made at four different temperatures, 
and from these data a curve was constructed by which the respiration at any 
temperature within the range of the research could be derived. 
After experiment the respiration plants were all dried and weighed air- 
dry and the respiration expressed per unit of dry weight. One gramme of 
dry Elodea has when fresh a respiration of 0°00125 grm. COe per hour at 
20°33 C. Therefore the dry 1:°955 grm. of Elodea used in this experiment 
involves a correction of 0°00244 grm. COz per hour. 
(c) Final Calculation of Assimilation—We have now the data for 
calculating the corrected Real Assimilation proper to 137 sq. cm. surface of 
illuminated Elodea under the conditions of the experiment, viz., illumina- 
tion = 5°7, average temperature of 20°3 C. and CO»-pressure in solution of 
0:0279 germ. COz2 per 100 cc. (about 15 volumes of COs per cent.). 
CO, disappearing in chamber per hour ............ 0:0268 
Subtract CO2 passing away in gas-bubbles......... 0:0024 
Apparent assimullagromeepecee screen: ---. 00244 
Add CO, calculated for respiration at 20°3 C. ... 0°0024 
Real assinilairo ms eesccey inset ios >. tos 00268 
The corrections for bubbles and respiration are not large under these 
medium conditions, and by chance they happen to be equal and antagonistic, 
so that the total correction has no effect. Of course, this will not be 
so with solutions richer or poorer in COs. 
This final number for the Real Assimilation of Elodea under this 
particular combination of environmental factors must be regarded as being 
