AUTO-THERMAL INTEGRATION OF CLIMATIC COMPLEXES 1 89 
These critical points are so widely apart (as much as 25° F. in 
various species) that anything like a generalized expression of the 
course or rate of growth of the higher plants would have but little value 
as a standard for the derivation of a unit for measuring the biologic 
effects of climate. It was therefore determined that evaluation of 
temperature exposures must for the present be made in terms of the 
activity of some single plant, and it may well fall out later that the 
generalization from a group of species may be of greater value. Many 
reasons make the data obtained from the growth of monocotyledons 
more valuable for the purpose mentioned, and several series of meas- 
urements of the rate of growth of wheat made by Koppen, deVries 
and others being available, these were used for testing the method pro- 
posed for estimating the temperature factor in the climate of a place. 
It is to be noted however that these measurements were made on the 
roots, "hypocotyls" or other parts of young plants, for the mcst part 
under equable conditions and it may not be assumed that the illumina- 
tion or humidity was in all cases under good control. The available 
data however show that growth elongation begins at about 40° F., 
rises very slowly in rate to about 63° F., then accelerates rapidly to 
86.5° F. with however a break or check between 80° and 83° F. The 
rate of growth at the highest temperature given was found to be 105 
mm. in 48 hours, but, above this, growth is checked and during a 
further rise of 11° the rate falls to 5.4 and comes to zero at 108° F. 
(see figure i). The first check in the rate of growth above 80° F. 
seems to have been found in several species and the most rational 
suggestion is that it may be attributed to some change in phase of the 
colloids, perhaps of the suspensoids. The final comprehensive drop 
follows a course highly suggestive of the procedure in which invertases 
and other specific substances are destroyed by high temperatures or 
their action inhibited. 
An extensive series of calibrations have already been begun at the 
Desert Laboratory and at the Coastal Laboratory in which the rate 
of growth of the internodes from the upper part of the stem will be 
measured in such manner as to give the possibility of some interpreta- 
tion of both the temporary and final retardation of growth in terms of 
physico-chemical processes. The data already at hand may be used 
for the present, and if our measurements differ from them the new 
factors may be applied to the figures obtained from the thermograph 
sheets in place of those expressed in the graph shown in figure i. 
