CLASSIFICATION OF AMERICAN WHEAT VARIETIES. 



47 



in Figure 18. In short brush the hairs are less than 0.5 mm. long, 

 in midlong brush from 0.5 to 1 mm. long, and in long brush more than 

 1 mm. long. 



All durum wheats and some varieties of common wheat, such as Bobs 

 and Prelude, have a short brush. A few very long hairs may be 

 present in a short brush. Humpback and* Mealy are varieties of 

 common wheat having a long brush. Both the size and the length 

 of the brush are very constant characters, probably the most constant 

 kernel characters aside from color and size. In machine thrashing, 

 part of the hairs of the brush frequently are removed. The brush 

 area of some varieties is here described as "collared" (Fig. 17, d). 

 Cobb (71) referred to this as an abrupt margin. This refers to the 

 presence of a distinct raised collar or flange of bran along the margin 

 of the brush area. This is most noticeable on shrunken kernels, but 

 is very distinct on normal kernels of a 

 few varieties, such as Goldcoin and 

 Champlain. 



PHYSIOLOGICAL CHARACTERS. 



Several characters of wheat varieties 

 of interest to growers can not be observed 

 in a morphological examination. These 

 differences are of a physiological or in- 

 ternal nature. They are of great eco- 

 nomic importance, but are of little value 

 in classification. Following the descrip- 

 tions of many of the varieties, therefore, 

 certain of the physiological characters here mentioned are considered. 



The leading physiological characters of importance in wheat 

 varieties are productivity, milling and bread-making values, resist- 

 ance to low temperatures, and resistance to diseases. 



PRODUCTIVITY. 



A comparison of yield is of value only in comparing different vari- 

 eties of wheat grown under identical conditions, as side by side, on 

 identical soil, or in one locality in the same season. Under certain 

 conditions it is possible for almost any variety to outyield all others, 

 and consequently an expression of yield is of little taxonomic im- 

 portance unless definite experiments at several points show a variety 

 to be significantly high or low in yield. Koernicke and Werner (133) 

 recorded the yields of the varieties grown at Poppelsdorf in the de- 

 sc'iption of each variety. In the present work the writers have men- 

 tioned productivity or yield following the descriptions of only a few 

 varieties, which experiments have shown to be distinctly high or low 

 in yield. 



Fig. 18. — Brush length. : a, Short ; 

 b, midlong ; c, long. (Natural 

 size and enlarged 3 diameters.) 



