2? The Philippine Journal of Science 1917 
due to variation in light intensity, especially since it is evident 
from their individual experiments that fluctuations in light in- 
tensity are accompanied by marked changes in assimilation. 
TABLE 11.—Hxperiments of Blackman and Matthaei on Helianthus. 
| 
Tem- Pan : : 
Experiment No. per- —_ Time. Light conditions. 
ature. : 
oc; a.m. 
Neder, cess. cca h waervbereottac 2804 0.0000 | .66-18.00 | Raining 
PF oii dh eshh ass aiuchiora nes J 20.8 | 0.0109 | 11.10-11.40 {|Cloud, haze. 
20.6 Heavy cloud. 
10.48, thin cloud. 
WeBviciete oo Go a a ere 22.3 | 0.0131 pester nae 24 10.52, slight rain. | 
; 1.00, cloud, haze. 
DEV Pac csecuteecns rouse chuske nan eoe 30.0} 0.0290 | 8.5 - 9.5 Brilliant sun. 
GENERAL DISCUSSION 
Since carbon dioxide assimilation is effected by light, it is 
to be expected that the temperature coefficients should have the 
magnitude ascribed to photochemical, rather than that ascribed 
to ordinary chemical, reactions. It should be emphasized that, 
owing to side reactions, after effects, and other disturbing 
factors, the exact determination of the temperature coefficients 
even of comparatively simple photochemical reactions is very 
difficult. For example, the photobromination of toluol was first 
found ** to have a temperature coefficient of 1.85. It has been 
shown,”* however, that this coefficient was merely the resultant 
obtained from a combination of photochemical and ordinary 
chemical reactions, the former having a low, the latter a com- 
paratively high, coefficient. 
From the above it is evident, that with so complicated a reaction 
as carbon dioxide assimilation, the fact that the temperature 
coefficient is within the limits of photochemical coefficients over 
wide ranges of temperature is very significant. 
A discussion of the temperature coefficient of carbon dioxide 
assimilation, if all disturbing factors were removed, is in the 
realms of speculation, but may be of interest. Plotnikow * has 
shown that photochemical reactions can be arranged in three 
groups in each of which all temperature coefficients are very 
similar. From this he assumes that there are in reality only 
* Bruner and Czarnecky, Bull. Acad. Sc. Cracovie (1910) 516, quoted 
by Plotnikow, J., Zeitschr. Phys. Chem. 78 (1911) 578. 
* For a discussion of this point, see Plotnikow, loc. cit. 
” Loc. cit. 
