24 
CoivORADO Experiment Station. 
canopy (Figure 15) and soil temperature records kept, but it was 
found that the shaded plants were but little, if any, better than the 
average. It was true of T912 in general that conditions of tem¬ 
perature were good, but that the crop was almost as badly affected 
by leaf-roll as in 1911. 
4 large cold frame (Figure 16) was placed over another small 
patch of hills with the idea that the additional heat might make the 
disease worse. Soil and air temperatures were higher but the light 
Figure 16.—Trying to hold some field plants still warmer by covering them 
with a large cold frame. The results were not what was expected. 
was more subdued and evaporation, and undoubtedly transpiration, 
were less. The plants, much to our surprise, were rather better than 
elsewhere in the field, and did quite a little growing late in the sea¬ 
son, after other plants were done. 
The effect of cultivation upon soil temperature is not to be 
overlooked. The heat rays pass through the air and warm it hardly 
at all. The air is heatetd, by radiation, from the surface of the 
earth which absorbs the sun’s rays. If the surface of a potato field 
is loose and dry it may be very hot, but. comparatively little heat 
goes deep into the earth, and when the sun has set, the earth and 
air above cool quickly. This is the condition in a desert, where the 
surface is loose sand, and this should be the condition in a potato 
field in a region of intense sunshine. Every barefoot boy knows 
how much hotter road dust is than solid earth. The road dust is 
letting less heat down into the soil, is hotter itself, and for the time 
being is giving off more heat by radiation. 
For three years we carried a pocket thermometer for the obser- 
N'ation of the temperature of soil and water. Under a bright sun, 
