COVERING OF S X O W , 



2G3 



March. April. May. 



Beyrout, Syria, . . . 61.3 65.3 71.3 



Alexandria, Egypt, . . 62.2 67.0 70.3 



Palermo, Sicily, . . . 54.0 58.6 64.8 



June. 



75.4 

 76.2 

 710.2 



Winter wheat generally succeeds best when the 

 ground is covered with snow ; and if this protection is 

 wanting, it is not unfrequently winter killed. It some- 

 times happens, also, that a covering of snow affects it 

 in such a manner as to destroy it entirely or in part ; and 

 this is the case when the snow is too compact, so as to 

 prevent the access of air for a considerable period. On 

 a clay soil the frost often acts mechanically, produc- 

 ing what is called heaving by the frost. Other influ- 

 ences of soil and culture affect the growth of wheat 

 probably to a greater extent than that of Indian corn, 

 and the same applies more or less to the other grains 

 mentioned in the second chapter. 



The northern range of these grains, particularly that 

 of barley and rye, is somewhat greater, and the differ- 

 ence may be stated at about five degrees of mean tem- 

 perature, which would embrace several degrees of lati- 

 tude. Barley grows further north than any other, but 

 both barley and rye will endure cooler and shorter 

 summers, and a somewhat poorer soil. 



