DISTINCTIONS IN CULTIVATED BARLEYS. 35 



ferent areas. The diameter of the culm is not serviceable, because 

 nearly related barleys have culms of approximately the same size. 

 The thickness of the walls of the culm is a note with a large experi- 

 mental error and therefore of questionable utility. 



The degree of exsertion of the spike is sometimes a varietal char- 

 acter but is not often useful. 



The number of culms per plant is to some extent a varietal char- 

 acter, but selections are so affected by season and location that it is 

 very difficult to use. The width of the leaves is useful in group 

 distinctions and sometimes in varietal separations. The length of 

 the leaves is much less dependable, and is serviceable only in rather 

 extreme types, The number of leaves varies with the groups, but 

 usually closely related strains possess approximately the same num- 

 ber of leaves. 



The density of the spike may easily be made the basis of many 

 separations. Often varieties that show no other differences are 

 widely dissimilar in density. The density of a selection varies 

 somewhat with season and location, but the mean is always sharply 

 defined and the fluctuations more or less parallel. In some strains 

 all spikes conform closely to the mean ; in others the range is greater. 

 This seems to be a varietal character and is constant even when the 

 plantings are made under widely varying climatic and soil conditions. 



The established taxonomic groups based on relative fertility were 

 found to be invariable under all extremes of American climate. 



The natural varieties in the deflciens group of Abyssinian barleys 

 seem more extensive than most classifications have indicated. From 

 barleys of this same region a group with a peculiar habit of floret 

 abortion has been isolated. 



The length and the width of awns vary, but they are so correlated 

 with other taxonomic characters that they are seldom useful in close 

 separations. 



The tenacity of the awn is frequently a varietal character unaf- 

 fected by location or season. 



The character of the basal bristle has been found to be stable 

 under American conditions. 



The toothing of the inner pair of dorsal nerves is much more 

 variable, but the variation is usually within definable limits. 



The length of the kernel, while influenced by climate, is a varietal 

 character. The lateral and dorsoventral diameters of the kernel are 

 varietal characters to some degree, but they are so influenced by con- 

 ditions of growth as to become confusing in most instances. 



The composition of the grain is a varietal character, but it is one 

 dominated by climate. 



There are two coloring materials in barley: Onej anthocyanin, is 

 red in its acid and blue in its alkaline condition ; the other, a melanin- 



