248 Report oF THE HorTICULTURAL DEPARTMENT OF THE 
shaded barley plants transpired less in the same length of time 
than did plants grown in the open. But the shaded plants trans- 
pired considerably more water per gram of dry matter than did 
the check plants. Further, much of the light under the cover 
is diffused light, as has been stated already, and plants transpire 
less in diffused light than in direct sunlight, as has been shown 
by Wiesner.® 
GENERAL APPLICABILITY OF SHADING AS A CUL- 
TURAL PRACTICE. 
The foregoing study of the effects of shading on the environ- 
ment of the plant and on the plant itself renders possible general 
statements as to the climatic conditions and the kinds of crops to 
which the practice is applicable. 
Shading as a means of conserving soil moisture is practically 
efficacious only within restricted limits. In seasons of abundant 
rainfall the more usual and less expensive methods of conserving 
soil moisture are sufficient and shading is unnecessary, assuming 
that exceptionally large size of the fruit is not a desideratum. 
In seasons of exceptional drouth, such as that of 1903 at Geneva, 
shading as managed in our experiments does not maintain suffi- 
cient moisture in the soil for the normal growth of the plant, 
though the practice is helpful to this end. But between these 
limits, that is under average climatic conditions, the practice is 
of very considerable helpfulness. It is not, however, nearly so 
efficacious as irrigation which, where practicable, would usually 
be cheaper. 
As a means of raising temperatures the practice is best appli- 
cable in those seasons and in those localities where there are the 
largest number of bright sunshiny days; it is also most efficient 
in that part of the day in which the sun’s rays fall most nearly 
from the zenith, that is, at mid-day. The practice is of little 
value in cloudy weather. It is of more value in the spring and 
early summer, when average temperatures are considerably below 
the optimum for growth, than in mid-summer, when this opti- 
mum is nearly or quite attained in the open. 
Shading is chiefly applicable to crops grown for aerial vege- 
tative parts. These parts grow much larger and at the same 
‘Cited by Vines, 8. H., Physiology of Plants, p.’ 109. 
