2 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 



of most of the modern taxonomists as well. The groups of Schuebler 

 (22) 1 , Seringe (23), Heuze (11, 12), Voss (25), Koernicke (13, 14, 15, 

 16, 17), Atterberg (2, 3, 4), and Beaven (5) involved variations in 

 density. In 1918 Harlan (10) offered an arrangement which elim- 

 inated the question of density from the major groups. It was re- 

 tained as a minor distinction only, because of the volume of the liter- 

 ature in which it had been used. Its complete elimination would 

 have left too little connection between the author's scheme and the 

 previous usage. j 



In classifying barleys, density is an obvious and attractive char- 

 acter. When confined to type forms the separations are ideal, but, 

 as with many things in taxonomy, its perfection depends on limited 

 material. The more material that is assembled the more the sub- 

 divisions of density have to be increased. Linnaeus (18) used the 

 name Hordeum distichon to designate the lax 2-rowed and H. zeo- 

 criton to designate the very dense 2-rowed forms. Schuebler divided 

 H. disticJion into erectmn and nutans. Eriksson (S) used genuinum 

 and patens to designate lax and dense subdivisions of erectum. 

 Linnaeus recognized Tiexastichum and vulgare as the dense and lax 

 groups of 6-rowed barleys. Koernicke divided Tiexastichum into 

 pyramidatum and paraUelum and recognized hrachyurum and macro- 

 terium of Alefeld (1) as dense and lax subdivisions of pyramidatum. 

 The finer the groups were made, the more confusing became the dis- 

 tinctions. The confusion indicated that, while there might be some 

 genetic distinctions, from a taxonomic standpoint there was no clear 

 separation. i 



In the mode of inheritance the situation is also complicated. As 

 a size character, the accounts are quite favorable as to its constancy, 

 and some varieties are traceable for centuries by this character alone. 

 In recent times Blaringhem (7), possibly following the lead of the 

 Svalof station, made quite elaborate studies of barley density in 

 France. Harlan (9) found density to be quite a stable character. 

 Regarding the- mode of inheritance, the studies, however, are largely 

 unsatisfactory. The taxonomic papers contain no comprehensive 

 measurement of density. Many of the inheritance papers are equally 

 inadequate. In many instances fertility and density are treated 

 together, as by Von Tschermak (24). Density has been regarded 

 as recessive by Blaringhem (7) and as dominant by Von Tschermak. 



The only paper which is directly concerned with the method of 

 study used in this article is that of BifFen (6), who obtained results 

 closely parallel to those presented herein. In three crosses to which he 

 paid particular attention, BilTen found the P\ generation to be slightly 

 more dense than the lax parent, although the numbers of individuals 

 in F t were small. The F 2 generation consisted in each case of plants 



1 The serial numbers in parentheses refer to "Literature cited," at the end of this bulletin. 



