DISTINCTIONS IN CULTIVATED BARLEYS. 17 



■vulgare. This is easily demonstrated by weighing kernels from side 

 and central spikelets. In the Hordeum sativum vulgare the lateral 

 kernels, compared with the central ones, are actually greater in rela- 

 tive weight than is the case in the Hordeum sativum hexastichum. 



Differences other than density are likely to be due to the nature 

 of the attachment of the lateral spikelets. Systematists describe the 

 barley spikelets as sessile. This is true in most cases, but it ap- 

 proaches an exception in Hordeum sativum hexastichum. In this 

 group the central spikelets are. sessile as usual, but the lateral ones 

 either possess an elongation of the base of the flowering glumes or 

 else are pedicellate. Among the barleys collected by the writer is a 

 Greek form in which the lateral spikelets are elevated upon a pedicel 

 that is over one-half as long as the length of the rachis internode 

 itself. This pedicel is jointed both at its attachment to the rachis 

 and at its attachment to the floret. It is the longer attachment of 

 the lateral spikelets that allows the characteristic radial arrangement 

 of Hordeum sativum hexastichum. Density is, however, a parallel 

 factor. The compactness of the spike forces the kernels to assume 

 certain relations. Both in Hordeum sativum hexastichum and in 

 Hordeum sativum erectum^ the kernels are placed at a much wider 

 angle with reference to the rachis than in Hordeum sativum vulgare 

 and Hordeum sativum nutans. The Swedish Plant-Breeding Associ- 

 ation at Svalof has considered the angle of the inclination of the 

 kernels as one of the more important of their notes. It is the opinion 

 of the writer, however, that, with rare exceptions, it will vary di- 

 rectly with the density, and is therefore superfluous if the latter 

 measurements be taken. 



In breeding, density has not been utilized as fully as its value 

 seems to warrant. Voss (25), Kornicke (15), and Atterberg (2), 

 have used it in group classification, and Atterberg, Blaringhem (8), 

 and the breeders at the Svalof station have used it in studies of 

 variation and purity, but in the opinion of the writer its possibilities 

 in the isolation of types and in the identification of strains have been 

 far from exhausted. 



In the years from 1909 to 1913 a close study of density was made, 

 both upon general farms and in experiment-station nurseries. In 

 this study, 100 spikes of each variety were taken without other 

 choice than that they were not diseased or dwarfed. On each of 

 these spikes 10 internodes of the rachis were measured; that is, the 

 distance was between six spikelets on one side of the rachis. From 

 these measurements the number of internodes per decimeter was 

 computed and this number taken as the unit of density. The for- 

 mula was then D=1,000-kL, where L was the length in millimeters 

 of 10 internodes of the rachis. 

 52783°— Bull. 137 3 



