xu, c,1 Brown and Heise: Carbon Dioxide. Assimilation 15 
These experiments were not used in Matthaei’s final curve for 
assimilation at different temperatures. With the exception of 
the first one they were performed in the last part of January or 
early in February, when the leaves were more active than at 
the time of the experiments on which the final curve is based. 
Varying the temperature between 25.3° and 38.3° seems to have 
had no appreciable effect on the rate of assimilation. Higher 
temperatures were detrimental. The figure for 11.0° is lower 
than for temperatures between 25.4° and 38.3°. This can readily 
be explained as due to differences in the seasonal activity of the 
leaves. Matthaei (p. 83, par. 5) says: 
The maximal assimilation of a leaf at 30° C. might be .0240 gramme in 
February, and in April be .0136 gramme, but a reduction in temperature 
to 11° C. would cause the same proportionate decrease in both cases. 
No evidence for the correctness of the latter statement is given. 
There is, then, no reason for assuming, as Matthaei does, that 
with eightfold intensity of light there is a rise in the rate of 
assimilation between temperatures of 11° and 25°. These ex- 
periments, indeed, agree with all of the previous ones in which 
reliance can be placed, in showing that with a given intensity 
of light, variations in the temperature above 3° produced no ap- 
preciable effect. 
We will now consider the figures for higher temperatures in 
Matthaei’s curve. These are presented in Table XI of her pub- 
lication and are summarized in Table 8 of the present paper. 
They are copied in greater detail than any of the previous ex- 
periments, as the figures for assimilation at 37.5° and 40.5° 
decrease markedly with each successive reading. The results for 
37.5° will be discussed later. The still higher temperature, 
40.5°, is evidently harmful and of no interest here. 
The first figure is that for 15°. Matthaei’s discussion of this 
point is as follows (p. 78, par. 7): 
Experiment LVI., 15° C.—The intensity of the light employed in this 
experiment was thirteen times unit intensity. The lowest temperature of 
the bath attainable was 11° C. (that of running water at that time of 
year), and, in consequence, the excess of light must not be great enough 
to raise the temperature of the leaf more than 4° C. 
Under these conditions the leaf decomposed .00703 gramme CO. per 
hour. Now it will be seen that in Experiment XXXVII, at 11° C., the 
intensity of the light used was eight times unit intensity, i. e., a little 
more than half that available in this experiment. The amount of CO. 
per hour was, however, .0072 gramme, and therefore this leaf 
at 15° C. must be exposed to nearly twice the light necessary for the 
assimilation which it has actually performed. 
