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32 Report oF THE HorticuLTuRAL DEPARTMENT OF THE 
EFFECT OF THE COVER ON THE ENVIRONMENT 
OF THE PLANT. 
The cover affects the growth of plants by modifying their phy- 
sical environment in certain respects, the principal changes being 
in temperature and moisture content of air and of soil, velocity 
of wind and intensity of light. These’ changes in environment 
bring about changes in the physiological activities of the plant 
and these in turn are the cause of the peculiar behavior and the 
gross results observed in practice. 
At the Station in 1903 records were made at 7 a. m., and 12 m. 
and 6 p. m., of the temperature of the air in the shade at the sur- 
face of the soil in both shaded plat and check. The thermometers 
were supported about two inches above the ground in a grape 
basket set on end, fastened to a stake and opening to the north. 
Other thermometers were set in the ground nearby to a depth 
of 3% inches to measure soil temperatures. The records of all 
these observations are shown, with other data, in Tables I and II, 
pages 2338, 235. 
EFFECT OF THE COVER ON THE TEMPERATURE OF THE AIR. 
The effect of the cover on the temperature of the air under- 
neath was to raise it somewhat except on very cloudy days, when 
there was no effect. During the period of observation, from May 
1 to June 30, there was only one day, May 20, when it did not 
appear to be at least a little warmer under the cover than out- 
side. This was a cold, cloudy day following a night temperature 
close to freezing. 
