248 NORTHEEN LIMIT OF GEASSES. 



periods as to become displaced, or to decay gradually, 

 if not suddenly,' and to require frequent renewal. This 

 departure from the native climate of these grasses is so 

 great at the plains beyond the Mississippi, as to require 

 a wholly new class ; and the European forms there cease, 

 to reappear only on the coast of the Pacific, in Oregon 

 and Washington Territories, where the English climate 

 is itself in some degree reproduced. 



The northern or low temperature limits of these 

 grasses appear nearly identical with those of wheat ; 

 and their liability to destruction by the cold of winter 

 alone, without regard to the lifting of the plant from 

 the soil, as in the case with wheat on tenacious soils, 

 does not greatly differ. The grasses will perhaps endure 

 a few degrees lower temperature. 



The high temperature limits are nearly the same as 

 with wheat also, taking the month of ripening for wheat 

 as the highest temperature for any month of the year. 

 The range of the English grasses is here little greater 

 than that of wheat, in this definition. As in cultivation, 

 they succeed when the mean temperature for July is 

 75° to 78°, while the limit of wheat is little aboye 70° 

 for the same month. In cultivation, without unusual 

 care, they would not diifer widely. 



There is a possible limit also in low summer tempera- 

 tures, especially if accompanied with a large amount of 

 moisture in the soil and atmosphere. We are not able 

 to give as precise limits for the English climate in this 

 respect as for wheat, though the grasses we have re- 

 ceived from there will not go many degrees lower than 

 wheat for the ripei^ing period, — probably not lower 

 than to 55° for the warmest month of summer, while 

 the same limit for wheat is above 57°. In the United 

 States it may not go so low ; though the question is 

 practically unimportant, as we have no districts below 

 60° for July. In cold and wet localities of the North- 

 ern States, the difficulty of preserving these grasses is 

 well known ; and, as in other directions of limit, they 

 fail gradually under measures of climatic disadvantage 

 not absolutely destructive. 



