XII, c, 1 Brown and Heise: Carbon Dioxide Assimilation 21 
The changes in velocity are readily explained as due to changes 
in the intensity of the light. When the values for assimilation 
are plotted with reference to light intensity they form a curve 
similar to that in fig. 3. 
Experiment 59 (Table 8) at a temperature of 37.5° and light 
intensity of forty-five units, shows a marked increase in the rate 
of assimilation over that shown in experiment 58 with the same 
light and a temperature of 30.5°. Table 8 shows that the rate of 
assimilation at 37.5° fell off very rapidly with successive read- 
ings. This shows that at this temperature there are compli- 
cating side reactions of considerable magnitude, so that it is not 
to be expected that a photochemical ratio would hold. The im- 
portance of side reactions will be shown in another connection. 
Moreover, one experiment under extreme conditions cannot be 
regarded as reliable when we consider the magnitude of the ex- 
perimental error with medium temperatures. For the above 
reasons we have thought it best not to attempt to draw any con- 
clusion from the experiment at the temperature of 37.5°. It 
is interesting to note that experiments 42 and 43 (Matthaei, 
Table VII) with light intensity of eight units and temperature 
of 38.3° do not show the decrease in the rate of assimilation that 
is seen in experiment 59. 
BLACKMAN AND MATTHAEI ON HELIANTHUS 
The work of Blackman and Matthaei has been quoted as 
showing a high temperature coefficient for Helianthus. Their 
statement is as follows: 
For a rise of 10°, the increase with cherry-laurel is 2.1 [0.0038 at 9° and 
0.0080 at 19° C.], while with Helianthus it is certainly bigger, perhaps 
2.5, but we have not exact data yet for giving the coefficient a precise value. 
The coefficient for cherry-laurel is based on Matthaei’s work, 
which we have previously discussed. The only basis that we can 
find for the one for Helianthus is a curve (in fig. 2, p. 414) that 
represents the initial assimilation-maximum for Helianthus at 
different temperatures. This curve is based on four figures 
that they give on page 413. In Table 11 we have selected from 
the full experiments the data on the readings mentioned. It will 
be seen that the lowest temperature was obtained while it was 
raining and the highest with brilliant sun. It is not evident why 
the changes in the rate of assimilation cannot be explained as 
” Blackman, F. F., and Matthaei, G. L. C., Vegetable assimilation and 
respiration IV. A quantitative study of carbon-dioxide assimilation and 
leaf-temperature in natural illumination, Proc. Roy. Soc. London B 76 
(1905) 402-460. 
