ae eee ee 
xu, c,1 Brown and Heise: Carbon Dioxide Assimilation 23 
three photochemical coefficients, and that these are 1.04-+-0.03, 
1.20+0.03, and 1.39+0.03. 
If carbon dioxide assimilation has one of these coefficients, 
the work of Matthaei on cherry laurel and that of Prjanischnikow 
on Typha, in direct sunlight, would indicate that it would be 
1.04. The coefficient, 1.07 from Kreusler’s work on Rubus, for 
temperatures between 15.5° and 25°, is in close agreement. The 
coefficients for Hlodea are higher, but this may be due to insuf- 
ficient data or complicating reactions. 
Apparently, photochemical coefficients hold for lower tem- 
peratures in cherry laurel than in Elodea. The low temperatures 
at which they hold for the former plant may be connected with 
the fact that this plant is an evergreen and that the experiments 
were performed during the colder months of the year. In other 
words, this plant apparently is adapted to carry on photosyn- 
thesis in a normal manner at low temperatures. The following 
statement made by Ewart * is interesting in this connection: 
It appears that all evolution of oxygen ceases in tropical plants between 
4° C, and 8° C., in warm temperate, subtropical, and water-plants between 
0° C. and 2° C., whilst in cool temperate, arctic, and alpine plants assimila- 
tion only ceases when the plants are frozen, i. e. at a few degrees below 
0° C. 
A summary of the temperature coefficients of carbon dioxide 
assimilation calculated from the work discussed in this paper, 
together with the temperature ranges over which they retain 
the order of photochemical coefficients, is shown in Table 12. It 
is evident that in many cases the limits could be greatly extended 
in both directions, without bringing the coefficients outside the 
range of photochemical, much less within the range of ordinary 
chemical constants. We have, however, limited ourselves strictly 
to the temperatures for which experimental data are at hand, 
and in which there can be no doubt of the order of magnitude of 
the coefficients. 
It is not surprising that carbon dioxide assimilation should 
show high coefficients at low temperatures, when we consider the 
possibility of complicating side reactions and the very high ratios 
shown by many physiological processes at similar temperatures. 
Keeping in mind the possibility of side reactions, the different 
methods employed by various investigators, and the correspond- 
ing experimental errors, the lack of perfect agreement in the 
coefficients listed above does not appear serious. 
“Ewart, A. J., On assimilatory inhibition in plants, Journ. Linn. Soc. 
Bot. 31 (1896) 401. 
