CLIMATIC RANGE OF GRAINS. 259 



Mexico, in winter ; so that the period of greatest growth 

 of the gramma or muskit grasses is various, being regu- 

 lated chiefly by the rains ; but even when dry they form 

 a very nutritive food for stock. 



On the western prairies but few valuable native 

 grasses are found. While they are allowed to grow 

 wild they cover the soil with a pretty close growth; 

 but when the turf is once broken it is very difficult to 

 reform it with the better English grasses, except around 

 low spots, or places well supplied with moisture. 



With respect to the climatic range of the grains, 

 such as wheat and Indian corn, and others spoken of in 

 Chapter II., little need be added in this connection. 

 With the exception of Indian corn, the grains are ex- 

 otics, and for the most part natives of a moist climate, or 

 came to us naturalized in a climate much more moist than 

 our own. They flourish best, therefore, in the cooler 

 parts of this country, though their range of climate, 

 with the exception of rice, is very great. In the more 

 southern portions they ripen before the hot, dry weather 

 comes on. The English grasses, as we have already 

 seen, are destroyed by it. 



For Indian corn, which is a tropical plant, there is no 

 southern limit of growth in this country, while the 

 northern limit to its profitable culture may be stated in 

 general at the point where the mean temperature is 

 about 68 Fahrenheit. The flexibility of its organization 

 is such that while in a warm climate it may grow for a 

 period of four or five months, or even more, in colder 

 latitudes it will ripen in two and a half or three months, 

 and rarely requires over four months. A small variety 

 is cultivated as far north as fifty-one degrees of latitude, 

 on the Red River. It requires great summer heats, but 

 will often succeed well in the northern states with a 

 cool and rainy summer, provided there is a week or two; 



