532 Smith . — The Temperature-coefficient of 
by the fact that an increase of light to four units increases the assimilation 
at the same temperatures. The value o-oo6i at 25 0 and L. In. — 4 is light- 
limited, as it is much lower than is obtained at the same temperature with 
greatly increased light (cf. assimilation o*ojoi at 23-7° and L In. == 26, Expt. 
LVII) from leaves at the same season of the year. On the other hand, 0-00365 
at 9-2° and L. In. = 4 is quite clearly limited by the temperature, since all 
the remaining values for the same light at higher temperatures are consider- 
ably greater. The value 0-00485 is obtained from an abnormal leaf (see 
previous argument, p. 525). The value 0-00465 at 11-4° is limited by tempera- 
ture, since an increase to temp. 25-2° is followed by a considerable increase 
of assimilation at the same illumination. The value 0-00505 with L. In. = 6 
and temp. 11-4° is limited by the temperature, as it lies, within the limits of 
probable error, upon the temperature-curve. The value 0-0063 a t 25-2° does 
not exist. It is an erroneous addition on the part of Matthaei to her sum- 
mary table and does not appear in her full tables or in her curve. 
The remaining values, 0-0070 at 15 0 and L. In. = 13; o-oioi at 23-7° 
and L. In. = 26 ; and 0-00136 at 30-5° and L. In. = 45, are all values limited 
by the temperature for reasons already fully set forth. Thus Brown and 
Heise’s curve is partly a light-curve, but principally a temperature-curve, and 
therefore does not show the relation between light intensity and assimilation 
as asserted by them. 
The Work of Pantanelli. 
In the paper by Blackman and Smith ( 1911 ) it was shown that Panta- 
nelli’s curve was of the usual compound nature, only the first part showing 
a true light effect, the later part showing probably the effect of limiting 
C 0 2 supply or possibly of temperature. Brown and Heise reject this 
explanation of Pantanelli’s curve and draw the curve again in such a way 
that they can interpret it as giving support to their thesis. Now in their 
exposition, in addition to minor matters of questionable soundness which are 
here omitted for lack of space, Brown and Heise have arbitrarily omitted 
from their curves all values above unit light. Yet Pantanelli conducted 
experiments at light intensities of 4, 9, 1 6, 25, 36, 49, and 64 units. It has 
been shown in our paper that while the values obtained in the highest 
intensities of light are justly omitted from the curve, giving smaller values, 
attributed to ‘ fatigue ’ of the chloroplast, yet the values at 4 and 9 units 
form an important part of the whole evidence. If it be asked why Brown 
and Heise have omitted, without any explanation or reference to the fact, all 
the results in light intensities greater than unity, the only answer at all 
possible is that these results are entirely fatal to their theory. Whether 
the stationary results at medium intensities of light or the depressed results 
at higher intensities are considered, there is here a long range of experiments 
in which the assimilation does not increase at all and the values cannot be 
