Photosynthesis : a Reply to Criticism . 
525 
perfectly justified in adopting these already well-established values at which 
temperature is limiting as part of her curve. This must be said, because 
Brown and Heise deal with the five experiments with light intensity of four 
units as an isolated set of experiments with no relation to previous values or 
results. These five experiments are part of the whole body of results and 
must be viewed in the light of them. They yield four separate temperature 
values, those for 9-3°, 11*4°, 24-8°, and -25*2°. . These values, as plotted by 
Brown and Heise, seem to exhibit inconsistency, but let us look at them in 
the light of previous results. The curve for four units of light must be 
allowed to have associated with it the temperature-values well established in 
the previous series, e. g. those at — 6° and at 04°. When these are added to the 
four values of the four-unit series itself there are obtained a series of six results 
which can only be consistently explained in the way adopted by Matthaei, 
namely, by the omission of the result for 24-8°, given by a leaf believed to 
be abnormal. We are not confined to the two alternatives offered by Brown 
and Heise, who say: ‘ If the figures for 11*4° and 24*8° are correct, there is 
very little or no rise in the rate of assimilation ; if the results for 9-2° and 
2,5*2° are reliable, there is a considerable rise.’ They conclude that ‘ the 
results are such that no reliable conclusions can be drawn from them \ 
Even if only the four values obtained at four units light are considered there 
is a third explanation, the one adopted by Matthaei, viz. that the results at 
9*2°, n*4°, and 25*2° are reliable and the one at 24*8° irregular. Reinforced 
by the values at — 6° and 0*4° her interpretation gives a consistent explanation 
of five out of six results, whereas the only conclusion from Brown and Heise’s 
theory is that the whole series is valueless, a very unlikely hypothesis. 
Matthaei’s treatment of the data is substantiated by her pointing out that 
the one value which is too low (at 24*8°) is given by a leaf that in a previous 
experiment had given an unusually low result for a less intense illumination. 
It is worth while to calculate the ratio for this particular leaf and compare 
assimilation at 4 units light 
it with the ratio for normal leaves. 
485 
The ratio . , 
assimilation at unit light 
The same ratio for the normal leaf 
for the leaf in question = - = 2*70. 
610 I ^° 
is = 2-77* The closeness of these two ratios supports Matthaei’s view 
that the experimental result at 24*8° is due to the lower assimilatory power 
of the leaf in question. Nor is this view upset by the fact that at unit light 
the results from the two types of leaves are close enough to be within the 
limits of experimental error. 
It is necessary here to consider the peculiar views held by Brown and 
Heise as to experimental error. They say * 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 V, Expts. 13 and 14 ’. 
