358 BOTANICAL GAZETTE [NOVEMBER 
ARRHENIUS, and that such processes possess temperature coeffi- 
cients, within the ordinary limits of environmental temperatures, of 
an order of magnitude of from about 2.0 to about 2.5. This may 
be regarded as a fundamental principle in physiology. 
When, however, many of these elementary or component 
processes are combined into a complex resultant, such as we have 
in physiological growth, for example, it is not immediately clear on 
a priori grounds that temperature coefficients of this same order of 
magnitude must obtain. RUSSELL” states rather authoritatively 
that “the effect of temperature on the rate of growth of a plant is in 
nowise like its effect in accelerating chemical change,” and cites 
the work of BraLoBLockr® in support ofthis view. The last named 
writer studied the influence of temperature upon the rate of growth 
of barley, and his results appear to show (see RUSSELL’s graph, p. 21) 
that the value of the temperature coefficient in this case alters 
markedly with the temperature itself. Considering, however, the 
fact that these results of BIALOBLOCKI appear to differ very 
markedly from those of the later workers who have dealt with the 
question, we are inclined not to give them such conclusive weight 
as does RussELL. In considering the matter before us, it is to be 
remembered that the principle of van’t Horr and ARRHENIUS has 
never been supposed to hold, even for simple chemical reactions, 
excepting between certain limits, and that these limits should not be 
expected to be the same for all processes. Furthermore, as has 
been emphasized by BLACKMAN,” RussELt (loc. cit. pp. 2° f.), 
MITSCHERLICH,” and others, the full possible: effect of a rise in 
temperature is frequently precluded by the failure of some other 
environmental condition correspondingly to alter. To illustrate, 
we may suppose (as BLACKMAN, loc. cit. 1908, suggests) that the 
*7 RUSSELL, E. J., Soil conditions and plant growth. London. 1912. 
* Bratostocxt, J., Uber den Einfluss der Boden wirme auf die Entwicklung 
einiger Culturpflanzen. Landw. Versuchsstat. 13:424-472. 1870 
9 Loc. cit.; also Biackxman, F. F., Optima and limiting ‘pean Ann. Bot. 
19: 283-295. 1905. 
* MiTscHERLIcH, E. A., Das Gesetz des Minimums und das Gesetz des abneh- 
menden Bodenertrages. Laindw. Jahrb. 38:537-552. 1900. 
Jber das Gesetz des Minimums und die sich aus diesem ergebenden 
Sdbbsaibigeinieed: Landw. Versuchsstat. 75: 231-263. 1911. 



