8EAS0X OF GROWTH 127 



and composition with the different varieties of wheat and 

 with cKmatic and soil conditions. 



165. Season of Growth. Wheat is grown successfully on 

 some of the higher altitudes at the equator, and from there 

 all the way to within 200 miles of the Arctic Circle. It does 

 best in a temperate climate where the rainfall is not less 

 than 20 inches, largely distributed through the growing sea- 

 son, and where the seasons are sufficiently long to allow 100 

 to 125 days of good growing weather free from frost. Spring 

 wheat matures in from 100 to 125 days from the time of 

 planting; winter wheat, in about 100 days from the beginning 

 of the growing weather in the spring. 



166. Classification and Varieties. Wheat may be classi- 

 fied in many different ways; as winter and spring wheat, as 

 hard and soft wheat, as bread and durum, or macaroni, wheat, 

 or by the botanical differences in the varieties. Wheat is 

 commonly divided into eight classes or types; but as onlv 

 four of these classes are of importance in the United States, 

 only these four will be discussed. 



In the first class, Triticum sativum vidgare, is found all 

 the common bread wheats, including the hard and soft win- 

 ter and the hard spring types. This is by far the most im- 

 portant class. The second class is the durum wheats, Trit- 

 icum sativum durum. It is distinguished by resistance to 

 drought and hardness of the grain. There are many varieties 

 of this type, though few are specially adapted to this countiy. 

 The third class is known as club wheat, Triticum sativum 

 compactum. The wheats of this type have short, compact 

 heads and produce very soft grain. They are commonly 

 grown in the Pacific states. The fourth class of wheat, Trit- 

 icum sativum dicoccum, is known as emmer, and is grown 

 only to a limited extent in this country. It is often errone- 

 ously called spelt. This differs from common wheat in that the 

 hull remains with the kernel when it is thrashed and the 

 stems are pithy instead of hollow. When growing, it is veiy 



