216 FIELD CROPS FOR THE COTTON-BELT 



limited by the dry period in the fall, making it shorter 

 than the frost limit data indicate. 



Corn is unique in being able to adjust itself to the grow- 

 ing season. In the extreme northern section of the United 

 States, some varieties mature in 80 days. In .no part of 

 the cotton-belt has corn been able to utiUze to advantage 

 a growing season in excess of 200 days. Most varieties 

 mature in 140 to 180 days. As a usual thing, the longer 

 the growing season up to a limit of 180 or 200 days, the 

 greater the yield of corn. 



265. Influence of climate upon habit of growth. - 

 Corn adjusts itself readily to changes in its environment. 

 We find, therefore, a marked correlation between climatic 

 conditions and its habit of growth. The greatest variation 

 is found in the size of the plant and in the time of maturity. 

 Southern varieties grow much taller than northern varie- 

 ties, and the stalks are more massive. Hunt ^ states that 

 " in general it may be said that as we go north or south of a 

 given latitude a variety becomes one day later or earUer 

 for each ten miles of travel, the altitude remaining the 

 same. That is to say a variety which ripens two weeks 

 before a killing frost in a given locahty would only barely 

 ripen if taken 140 miles farther north, the altitude remain- 

 ing the same. Care should be taken, therefore, in selecting 

 new varieties, to get them from the same latitude. If 

 obtained from much farther north they may ripen too 

 early and consequently be too small. If obtained much 

 farther south, they may not ripen." 



' Hunt's "Cereals in America," p. 205. 



