30 BULLETIN 622, U. S. DEPARTMENT OF AGRICULTUEE. 
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 nimierous 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 sub varieties. 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 
by 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. 
