BUNTON: XEROPHYTIC VEGETATION. 



185 



Monthly maximum temperatures for the year 1904, with dates. 



January 18 65° 



February 9 72° 



March 2 82° 



April 10 79° 



May 24 93° 



June 23 99° 



July 29 102° 



August 24 95° 



September 9 103° 



October 3 87° 



November 18 73° 



December 31 68° 



Monthly minimum temperatures for year 1904, with dates. 



January 25 — 2° 



February 19 3° 



March 3 6° 



April 17 25° 



May 14 34° 



June 11 50° 



July 26 54° 



August 22 50° 



September 14 41° 



October 25 25° 



November 11 11° 



December 26 4° 



Another ecological factor which has much to do in shaping 

 plants is the wind. On the prairies the wind has full sweep ; it 

 blows most of the time at a rapid rate and tends to dry up what- 

 ever vegetation there may be in its path. No definite statement 

 can be made as to the velocity of the wind of this special local- 

 ity. In the following table, however, are shown some of the 

 results of observations made by Stevenson, of Edinburgh, upon 

 the increase in velocity of the wind with the height above the 

 ground, as given in Schimper's Plant Geography : 



Height of instrument 

 al>oveprroun(l, in feet. 



V2 .... 



Velocity of wind 

 in miles per hour. 



6.83 



2% 8.73 



41/3 9.77 



91/2 10.45 



14 10.54 



25 11.54 



50 12.21 



Height of instrument 

 aboveground, in feet. 



V2 

 31/2 



9 

 14 

 25 

 51 



Velocity of wind 

 in miles per hour. 



.... 9.8 



12.4 



. ... 13.8 



14.3 



15.0 



16.3 



Height of instrument 

 aboveground, in feet. 



IVs .... 



31/2 .... 



9 



14 



25 



51 



Velocity of wind 

 in miles per hour. 



.... 22.2 



.... 25.6 



.... 31.9 



33.7 



37.1 



42 . 7 



From the above tabular statement it is quite clear that plants 

 that are only slightly raised aboveground experience the effects 

 of the wind much less than tall plants, and especially trees. 



