xu, C,1 Brown and Heise: Carbon Dioxide Assimilation 13 
limiting factor in the critical experiments begins as follows (p. 70, 
par. 2): . 
When the intensity is doubled, the assimilation at 0.4° C. is unaltered, 
but an increase is produced at the other temperatures, numbers almost 
identical being obtained for all of these. 
The temperature is below that which we are considering. It 
-may be said, however, that with unit intensity of light the result 
at 0.4° is very similar to those obtained at all higher temperatures 
and so is greater than would be expected from the more complete 
results recorded in Table 1 and plotted in fig.1. This figure shows 
an increase in assimilation of considerably more than 50 per cent 
between 0.4° and 3.6°. Doubling the intensity of light did, 
however, increase this apparently too high result in Table 2 for 
unit intensity of light at 0.4°. 
The paragraph, under discussion, continues: 
When four times the light is used we find a similar phenomenon. The 
assimilation at 9° C. is no greater than that corresponding to twice the 
light, for the temperature exerts its limiting effect and the leaf can 
assimilate no more. At 11° C. a higher number is obtained, which, however, 
- is not so great as that obtained at 25° C., showing that the leaf can make 
use of more light than is given by L. In. = 2, but it cannot use all that 
of Li’ Im 4, 
The above conclusion is reached by discarding the figure for 
light intensity of four units and 24.8° and regarding those at 
9.2° and 25° as accurate. If the single low figure at 9.2° is 
not reliable, her argument fails. It has already been shown that 
these figures cannot be regarded as reliable enough to have 
positive conclusions drawn from them. 
The percentage of increase between the figure for 9.2° and the 
one for 11.4° and four units of light is, moreover, within the 
possible limits of experimental error indicated in our Table 5, 
experiments 13 and 14. Such differences are probably not due 
to errors in measuring the carbon dioxide absorbed, but might 
well be due to variations in leaves and light. Under such con- 
ditions one experiment is certainly not a sufficient basis for 
conclusions, 
Continuing Matthaei says: 
Sixfold light gives practically the same results as fourfold shal for 11° 
C., showing that the maximum has been attained. 
If the percentage of increase is calculated it will be found that 
at 11.4° raising the light from one to two units, or 100 per cent, 
increased the assimilation 70 per cent; raising the light from 
