30 BULLETIN 622, U. S. DEPARTMENT OF AGRICULTURE. 



these separations in a later publication. In the varieties at present 

 grown in America, separations are most difficult in the lax forms 

 of the common 6-rowed barleys. In general, there are two groups, 

 the Manchuria- Oderbrucker and the Coast. These groups are sepa- 

 rated by the longer, heavier grain and the more tenacious awn of the 

 latter. Within a group such as the Manchuria, identifications must 

 be based on combinations of minor characters, such as the density 

 of the spike, the nature of the hairs on the rachilla, the length of 

 grain, and, if necessary," distinctive culm characters and the length 

 of the growing season. 



SUMMARY. 



The variations that occur in barley are of importance to the 

 student, agronomist, plant breeder, and pathologist. They offer a 

 wide opportunity for selection, breeding, and studies of disease 

 resistance. In barley the forms are unusually numerous and clearly 

 defined. The number and character of the types existing are more 

 concisely indicated by a classification of variations than in any 

 other way. 



The groups of barley have been arranged upon the basis of species, 

 varieties, and subvarieties. Only major characters have been used in 

 describing species and varieties ; less important characters have been 

 utilized in describing subvarieties. Under each subvariety there may 

 be an unlimited number of agronomic varieties. Four species and 

 32 varieties are recognized. 



All groups have been made to conform with previous usage as far 

 as possible. One of the principal aims of the writer of this bulletin 

 has been to state clearly the form or group intended to be described 

 bjr each published name. Except for their historical significance, 

 the subvarieties would not have been continued, and no forms have 

 been added to them. 



Four varieties have been added. 



Lists of rejected terms and varieties are included. 



The keys can be adapted to the identification of thrashed grain 

 by a number of characters. In the common agronomic varieties the 

 chance of error in the identification of thrashed grain is slight. 



