\ 
1916] CURRENT LITERATURE 83 
growth, however, as is frequently true in chemical and physical processes, the 
coefficient falls as the temperature rises above o 
At temperatures above 29° C. the initial rate is not maintained, but 
fluctuates or falls as time elapses, the well known time factor of BLACKMAN. 
At 30° and 35° C. the initial fall in rate is followed by a rise, which in turn is 
followed by a continuous fall, while at 40° C. the fall in growth rate is continuous 
with the elapse of time. This is comparable to the respiratory intensities at 
higher temperatures as determined by Ku1yPER.” 
The growth minimum for the organ studied is —2° C. and the maximum 
44°5C. In lieu of the errors involved in the old conception of optima, as 
shown by BLACKMAN and confirmed by many others, LEITcH proposes a new 
definition for optimum temperature in relation to any process in the organism, 
namely, the highest temperature at which no time factor enters. For the organ 
studied the point is between 28° and 30°C. A fourth cardinal point is defined, 
namely, maximum-rate one ipdesnsit as the temperature at which the process attains 
its highest intensity, which is 30°3 C. in this organ. 
It is to be regretted that the author did not have mine 
the excellent work of LEHENBAUER (thesis, Tllincis, Bi a ita | in Spa 
part, obtained similar results and arrived at similar rare —Wm. 
ROCKER. 
Subalpine flora.—In continuing a series of phytogeographical papers, the 
first of which was recently reviewed in this journal, RypBERG* has discussed 
the forests and grasslands of the zones immediately below the alpine. He 
distinguishes two principal areas in the Rockies separated by a break in the 
range occurring in Wyoming about where the Union Pacific Railroad crosses. 
This break divides the portion of the region under discussion into the northern 
and the southern Rockies. The northern Rockies extend from the Yukon 
southward, and are made to include the Sawtooth Mountains of Idaho, 
Alberta. They are further extended to include the Black Hills and smaller 
chains in their neighborhood. Over this area RypDBERG says the flora is prac- 
tically homogeneous, and includes among other trees not found in the southern 
part Larix occidentalis, Abies grandis, Tsuga heterophylla, T. mertensiana, 
Thuja plicata, Taxus brevifolia, an several species of Betula, Salix, and Populus. 
In a further analysis of the flora, species exclusively southern and those com- 
mon throughout the range are noted. Notes are also made of habits of growth 
and peculiarities of distribution of the more important trees and of the variation 
of altitudinal range of the zones. 
er Gaz. eles IgIo. 23 Bot. Gaz. 59:64-65. 1915. 
YDBERG, P Phytogeographical notes on the Rocky Mountain region. 
IV, ea of go in le and montane zones; V. Grasslands of the subalpine and 
montane zones. Bull. Torr. Bot. Club 42:11-25, 629-642. 1915. 
