122 THE ROYAL SOCIETY OF CANADA 
The greatest drought was from June 16th to July 15th. Briggs 
& Shantz!§ have adopted the five-day period in their researches on 
evaporation at Akron, Colo., for the months of April to September 
inclusive, during the two years 1912 and 1913. During 1912 there 
were 30 five-day periods with evaporation in excess of rainfall out of a 
total of 36 and in 1913 there were 33 with evaporation in excess of 
rainfall. The longest drought in 1913 covered 31 five-day periods. 
The average evaporation’® at Lincoln, Nebraska, from May 
to October for the 16 years 1895-1910 inclusive was 34-56 in., while 
the rainfall for the same months was 23-24 inches. 
At Tucson, Arizona, the average rainfall for 15 years was 11-74 
inches while the normal annual evaporation amounted to 90 inches. 
WIND. 
Wind affects plants in several ways. On mountain tops and 
on sea coasts the constant blowing of the wind has a dwarfing effect 
on many plants, producing the “cushion” type of vegetation while 
a region that is subject to violent gales is unsuited for the growth 
of broad-leaved trees. Attempts to establish trees in Sable Island 
proved unsuccessful. A region subject to winds may be expected 
to contain a large percentage of anemophilous plants in its flora 
and at high altitudes vivipary may result. Wind also plays a prom- 
inent part in the dissemination of many types of fruits. Further, 
wind greatly increases the evaporation of water from the surface 
of the soil and stimulates the rate of transpiration in plants. Some 
estimate of wind-effects in different regions may be gained from a 
survey of the total number of miles travelled by the wind during 
each half year period and from observations of the maximum velocity. 
A high wind occurring when trees are in full leaf will be much more 
disastrous in its effects than it would be if the leaves have fallen. 
Some figures relating to winds are given in Table XIII. 
18 Briggs, L. J. and Shantz, H. L.—Relative Water requirements of plants. 
Journ. Agr. Research III. 1-64. PI. VII, 1914. 
19 Loveland, G. A. and Perin, S. W. Evaporation from a free water surface at 
Lincoln, Nebraska, 25th An. Rep. Agr. Exp. Sta. Neb. 1912. 
