1917] CURRENT LITERATURE 517 
in which the temperature coefficient for a rise of 10° C. is 2.1. In Helianthus 
tuberosus it was 2.5. Below 25° C. the initial rate is maintained, but above that 
temperature it falls off regularly. The higher the temperature the more rapid 
is the falling off. The falling off at any given temperature is most she at 
first and subsequently becomes less rapid. 
Since it is thus impossible to measure the highest possible assimilation at 
high temperatures, BLACKMAN estimates it by plotting his experimental results 
below 25° C. (a van’t Hoff curve in which Qyo= 2.1) and continuing the curve 
by assuming that the same rule is followed above that temperature. That 
this curve represents the initial rate above 25° C. is confirmed in BLACKMAN’S 
opinion by plotting on this same diagram (the abscissae now having a time 
significance instead of a temperature significance) the values obtained for the 
assimilation rate at higher temperatures, and continuing these curves back toa 
point representing zero time. It is thus found that the position representing 
zero time for each curve is also that representing the temperature at which the 
readings were taken. 
n this basis BLACKMAN concludes that there seems to be reason for the 
preliminary acceptance of the theory that the initial values of assimilation 
above 25° C. follow the van’t Hoff curve as they do below that temperature. 
JORGENSEN and STILEs seem disposed to defend BLACKMAN against all criticisms 
on this point. It must be remembered, however, that CoHEN-STUART has 
shown that, according to the van’t Hoff law itself, values of Q,. are not constants 
and that the velocity is not an exponential function of the temperature. 
Kutypers found that such a method as BLACKMAN used on carbon assimilation 
did not apply to respiration. Lrrrscu® has also found that it does not apply 
to temperature and rate of growth. 
In regard to the light factor, the conclusion is reached that “‘ where temper- 
ature and carbon dioxide supply are in excess the rate of assimilation is in 
direct proportion to the intensity of illumination.” In the case of cherry laurel 
during the middle of an August day (temperature 29°5 C.) the maximum 
assimilation was possible with 36 per cent of full sunlight, while in the case of 
Helianthus 69 per cent was necessary 
Assimilation is shown to increase directly with carbon dioxide supply 
until some other factor becomes the limiting one. When this point is reached, 
assimilation remains constant with further increases in carbon dioxide up to 
©.0536 per cent. Above this point the rate of assimilation falls off rapidly. 
BLACKMAN’s interpretation is that this is due to the sasieds effect of the 
strong CO, on the protoplasm. The reviewers state that ACKMAN Care- 
fully avoids premature conclusions and tries to find Se euia expressions 
which will embody all his experimental results.’ 
4 Konn. Akad. Wetans. Amsterdam. Proc. Sec. Sci. 14:1159-1172. 1912. 
5 Rev. Bor. GAZ. 50:233~234. I9g10. 
6 Ann. Botany 30: 25-46. 
