400 THE CLOVERS 



vation. The lime content has steadily declined and with the decline 

 red clover culture has become increasingly difficult. Many large 

 regions that grew red clover twenty-five or thirty years ago can no 

 longer produce it without the use of lime. 



Agricultural Varieties. While there are several regional 

 strains of red clover which differ in small detail, there are only two 

 recognized varieties with a marked difference. They are usually 



FIG. 173. Sowing red clover in fall wheat with special grass-seed drill. 



known in the market as medium red clover and mammoth clover. 

 The principal differences are: (1) Mammoth clover is about two 

 weeks later in blossoming. (2) The stems of medium red clover are 

 usually hollow, and those of mammoth clover are solid. (3) 

 Medium red clover will usually make both a hay crop and seed 

 crop the same season, while mammoth clover will make only one 

 crop. 



A form differing somewhat from common medium red clover, in- 

 troduced from Russia, and known as Orel, has been tried with con- 

 siderable success in the United States. The United States Depart- 



