New York AGRICULTURAL EXPERIMENT STATION. 237 
DISCUSSION. 
Among the changes in environment advantageous to the plant, 
the great decrease in the movement of air appears to be the most 
important. The cover acts as a cloud, confining a layer of air 
underneath and protecting it in large measure from change by 
air currents without. This results in a greatly reduced evapora- 
tion—also transpiration as will be seen later—accompanied by 
an increase in temperature and in moisture content of air and of 
soil. The increase in temperature of the air would of itself 
increase evaporation while the increase in moisture content 
would diminish it; but far out-weighing either or both of these 
is the greatly reduced evaporation due to the diminished move- 
ment of the air. This decrease in evaporation accounts in part 
at least for the increased temperature of the soil, since evapora- 
tion is a cooling process. 
The increased temperature of the air is due to the gradual 
accumulation of warmth in a relatively slow-changing atmos- 
phere and this in spite of the fact that the white cover would 
intercept and reflect a part of the sun’s rays. The increased 
moisture content of the air would be to some extent instru- 
mental in preventing the radiation of the earth’s heat back into 
space. At the same time the cover probably retards to some 
extent the upward movement of the warmer, lighter air under- 
neath. The heat radiated from the earth is also conserved for the 
use of the plant in larger part than it is in the open. 
EFFECT OF THE CHANGED ENVIRONMENT ON THE 
PLANT ITSELF. 
The effect of the changed environment on the development of 
the plant itself will now be considered. | 
EFFECT OF SHADING ON VEGETATIVE GROWTH. 
At the Station the cover was placed in position April 30, at 
which time the new leaves were just starting. As the season 
advanced it was evident that the shaded plants were making the 
more rapid growth. 
The promoticn of growth by shading showed itself to a less 
marked extent in the forwarding of the season of coming into 
Lloom, as is shown in the following table: 
