68 
JOHN H. EHLERS 
Miyake and Matthaei. In making comparisons it should be borne 
in mind, however, that Matthaei's material had previously been kept 
at a uniform temperature from io° to i6° C, and that Miyake's 
experiments were made at Tokyo where the mean temperature for the 
three winter months is 3.8° C. and the minimum — 6.5 (Kusano (12)), 
while the plants from which Ewart obtained his material had been 
exposed for three weeks to temperatures falling below — I5°C. Ewart 
ascribes the inability of these plants to assimilate CO2 at 1° C. to 
the inhibiting effect of the extreme temperature to which they had 
been exposed. The same plant material, when brought to a temper- 
ature of 15° C, showed weak assimilation within a few hours and 
quite active assimilation within eight hours to one day. The long 
latent period of recovery, according to Ewart, indicates that the 
exposure had nearly reached the plant's limit of resistance. Un- 
fortunately Ewart does not state how long the tests for assimilation 
at 1° C. lasted. One gains the impression that the tests were of short 
duration. It is entirely possible that, had the plants been exposed 
to a temperature of 1° C. for a longer time, the inhibiting effect of the 
previous extreme temperature would have been overcome and assimi- 
lation begun. The contradiction between Ewart's results on the one 
hand and those of Matthaei and Miyake on the other is, therefore, 
more apparent than real. 
Bearing in mind the assimilation curve obtained by Matthaei, 
the application of the results of the present investigation becomes at 
once apparent. Ka.nitz (10) has shown that the law of van't Hoff 
(32), that for every rise of 10° C. the rate of reaction is doubled or 
trebled, holds for the results obtained by Matthaei for temperatures 
between 0° and 37° C. assuming other conditions favorable. For 
temperatures from — 6° to 0° C. the rate of increase is very much 
greater. The assimilation curve in Matthaei's work shows an increase 
in assimilation from 2 mmg. of CO2 per 50 sq. cm. per hour at — 6° C, 
to 18 mmg. at 0° C, — an increase of 900 per cent. Since an increase 
of 6° C. in the temperature of the leaf due to the absorption of radiant 
energy is not at all uncommon and higher temperature differences are 
often found, the increase in assimilation resulting therefrom is of 
very great importance and goes far toward explaining the accumu- 
lation of reserve food material by evergreen trees. 
University of Michigan, 
Ann Arbor. 
