HIGH AND LOW TEMPERATUBES. 247 



temperature alone, and the dry extremes are very 

 injurious, and sometimes absolutely destructive. What 

 precise measures of low temperature destroy these 

 grasses, it is difficult to say ; but every alternate year 

 affords some locality in which the cold is so great as to 

 destroy the Timothy and orchard grasses. A continu- 

 ance of cold for some days below zero of Fahrenheit, 

 and with a minimum of 20 below zero, is undoubtedly 

 certain to be fatal, if the surface is exposed to the air, 

 and is without protection by snow or otherwise. 



There is apparently little difference in the hardiness 

 of the principal cultivated grasses in resisting the tem- 

 perature extremes. Low temperature alone may 

 destroy them in all the elevated portions of the New 

 England States and New York, and in Wisconsin and 

 some parts of Illinois. In most cases the destruction 

 of the three principal grasses occurs at the same time, 

 and no singling out of particular species is remarked. 



In the direction of high temperatures there appears 

 no definite limit of this sort, or none depending on 

 single extremes ; but all these grasses fail when the 

 mean temperature of the summer months attains to 80. 

 They have but a variable and uncertain success in Vir- 

 ginia, and in all the states south and westward they are 

 still less reliable, or fail altogether. As they are all 

 perennial in the highest sense, the whole year arid all 

 its extremes must be taken into the account. They 

 cannot, as in the cereals, choose a portion of the year 

 only, and adapt their requirement of time to the tem- 

 perature. In this respect they differ most widely from 

 a very important class of native grasses, which occupy 

 the arid portions of the continent. 



In further notice of the limitations of the European 

 grasses, the humidity of climate must be considered. 

 The dry extremes of many of the states where they 

 may generally succeed are quite injurious or destruc- 

 tive in many cases, and this is especially true of the 

 states at the West, where the soil is less tenacious and 

 retentive than at the East. They fail to form the charac- 

 teristic turf there, and are so much injured by those dry 



