[ADAms] CLIMATIC FACTORS IN RELATION TO PLANT LIFE kite 
TABLE VII. 
SUNSHINE, DIFFUSE LIGHT AND DARKNESS. 
Mavy-Ocr, 1912. 


Sunshine Diffuse light Darkness 
hours. hours. hours. 
Edmonton 
MEEPS SUS Shee er Ue es iar 1,299 13 1,740 
Toronto 
ILE SERRE eerie ee 15223 1,296 1,897 


The present method of reckoning sunshine in hours expresses 
only a part of the result. For example, the temperature in the sun at 
Ottawa on April (5th, 1916; was 8 0F at 2°p:m, 76° Fat 3p.m;,, 
77° F. at 4 p.m., and 68° F. at 5 p.m. and on the 16th April, 1916, 
the temperatures were 47° F. at 6 a.m., 52° F. at 7 a.m., 61° F. 
at 8 a.m., and 73° F. at9 a.m. In expressing the result as sunshine 
hours the three hours from 2 to 5 p.m., have the same value as the three 
hours from 6 to 9 a.m. A better method would be to multiply the 
number of hours of sunshine by the average temperature in the sun 
during the period in question after deducting 32° and call the figures 
“‘sunshine-degrees.”” The number of sunshine degrees in the case 
quoted for the three hours 2 to 5 p.m., would be 134% and the number 
for the other three hours 6 to 9 a.m., would be 77 sunshine degrees. 
PRECIPITATION. 
Equally with temperature the amount of rain is of fundamental 
importance in relation to plant life. Not only is the total amount of 
rain that falls of great importance but its distribution in time. A 
torrential rainfall such as occurs in connection with a thunderstorm 
when an inch of rain may fall in one hour has not the same permanent 
effect as the same amount of rain falling continuously for six hours. 
In the former case, especially on a sloping surface or clayey soil a 
large proportion of the water runs off into the nearest stream instead 
of being absorbed by the soil as it falls. 
On the other hand a slight rainfall of one-hundredth or even 
one-tenth of an inch occurring during the warmer months only wets 
the surface soil and does not add to the moisture of the deeper layers. 
It is consequently soon lost by evaporation. Shreve “ states that at 

4 Shreve F. Rainfall as a determinant of soil moisture. Plant World, 17 Jan 
1°14 
