1914] HASSELBRING—EFFECT OF SHADING 263 
effect of the cheese-cloth tent, therefore, appears to be not only. to 
reduce the total amount of light available to the plants, but also to 
transform a large proportion of the direct light into diffuse light. 
The plants growing within the tent have available for photo- 
synthesis less total light than the plants growing outside, but a 
larger proportion of this light is diffuse. 
TEMPERATURE 
The temperatures in each of the two stations were recorded by 
Fries thermographs placed in shelters so constructed, with double 
roof and open sides, as to protect the instruments from the direct 
Tays of the sun and from rain without hindering the free circulation 
of air. The thermographs had been carefully adjusted during a 
few weeks’ trial previous to the beginning of the experiments. After 
having been placed in the field, they were daily compared with 
Standard thermometers whose bulbs hung near the bellows of the 
instruments. The thermographs agreed very closely with the 
thermometers throughout the experiment, and required very little 
further adjustment. 
The average daily temperatures during the course of the experi- 
ment were obtained by integrating the records for each day with a 
Planimeter. The results thus obtained, together with the differ- 
ences between the daily average in the tent and in the open, are 
given in table III. The records are given in Fahrenheit degrees 
since the instruments recorded in that scale, but the values have 
also been calculated in Centigrade degrees, which are given in the 
last two columns. 
Table III shows that there was no marked difference between 
the temperature within the tent and that outside. The difference 
Was usually less than one degree. Moreover, it was sometimes 
Positive and sometimes negative. ‘The sum of the differences for 
the total period is only 7°67 F. The average daily excess of the 
perature outside the tent over that inside was therefore approxi- 
mately of14. This is contrary to the results of SrEwART,’ who 
found that in the Connecticut Valley the average daily temperature 
‘ *Stewarr, J. B., The effects of shading on soil conditions. U.S. Dept. Agric., 
“reau of Soils, Bull. 39. 1907. 
