268 BOTANICAL GAZETTE [APRIL 
tain, bringing the mean temperature of Colorado Springs lower than 
it would be if inversion did not take place. The data for the last 
three sets of localities in the table are for one season only. 
TABLE V 
DECREASE IN TEMPERATURE WITH INCREASE OF ALTITUDE 
Decrease of tem- 
Stations compared perature per 1000 
feet (in degrees F.) 
. 
Pike’s Peak—Colorado Springs*............... 3-4 
Pike’s Peak-Lake Moraine*....... 2.3... 0%.. 4.3 
Lake Moraine—Colorado Springs*............ 2.6 
Boulder—Arapahoe Peak at timber linet....... aie 
Denver Oregano ees 2:6 
Boulder—Redrick LakeP oon. 2). os. 2:2 
* Data from Annual Summary of Colorado Division of the Climatological Service. 
+ Data from Younc, Rosert T., Forest formations of Boulder County, Colorado. Bot. GAZETTE 
46: 321-352. 1907. 
ata from RAMALEY, FRANCIs, AND’ Roppins, W. W., Studies in lake and streamside vegetation. 
t. Redrock Lake near Ward, Colorado. Univ. Colo. Studies 6:133-168. 1900. 
INVERSION OF TEMPERATURE.°—This phenomenon is common in 
mountainous regions, being particularly noticeable in the spring and 
autumn. The valleys and canyon bottoms are often cooler than the 
adjacent hillsides; the plains are cooler and have greater diurn 
range of temperature than the overhanging foothills.’ 
A comparative study of temperatures of the University of Colorado 
campus® and the mesas near by, 415 feet higher, showed for May 
1908 the mean monthly difference in temperature to be 2°6 higher 
on the mesas than on the campus. Furthermore, the last frost in the 
spring was 16 days later on the campus than on the mesa. This 
inversion is undoubtedly present all along the foothills. Mesas have 
a milder climate than adjacent plains, and the early spring vegetation 
is in advance of that on the plains. On account of temperature 
inversion in canyons and gulches, high altitude forms find their lowe 
6 HANN, I. ¢., p. 252. 
7 In the southern Alleghenies, CaickErtne (J. W., Jx., Thermal belts. Amer. 
Meteor. Jour. 1: 213-218. 1884-85), quoting SrLas McDowett of Franklin, Mee 
County, N. C., describes the presence there of a “thermal belt” or “frostless 20P¢ 
upon the mountain sides, commencing at about 300 feet vertical height above the 
valley and having a breadth of 400 feet vertical height. 
§ RaMALEy, FRANCIS, Climatology of the mesas near Boulder, Colo., in Studies 
on mesa and foothill vegetation. Univ. Colo. Studies 6:11-49. 1909. 
