28 BULLETIN" 10^4, U. S. DEPARTMEIsTT OF AGRICULTtfRE. 
LEAF CHARACTERS. 
The principal parts of the leaves of wheat plants are the sheath, 
blade, ligiile, and auricle. None of these parts usually show differ- 
ences which are of even minor value for distinguishing cultivated 
varieties. 
The blades of wheat varieties vary considerably in their dimen- 
sions, in the shade of green color, and in the angle to the culm main- 
tained during the successive periods of plant growth. These differ- 
ences, however, are apparent during only a short period. As the 
plant matures, the blades dry and frequently break off. Practically 
all cultivated varieties normally have three leaves, although this 
sometimes varies under unfavorable or very favorable conditions. 
In this bulletin very little use is made of leaf characters. A few 
varieties are noted as having especially broad or narrow blades or as 
being pubescent. 
Koernicke and Werner {133) and others have described the color 
of the blades of both the seedlings and the partly grown plants. 
This also was attempted in the present studies, but the differences 
were found to be so slight and undependable that no definite classes 
could be established by using the character. No two persons can 
agree as to the various shades of green shown, by the blades of wheat, 
even when a standard color chart is used. The color varies with the 
condition of the plant as affected by the temperature, the soil mois- 
ture, and the soil solution. The appearance of the color is changed 
by the character of the venation and of the blade surface. The plants 
appear to have a different color in the sunlight than in the shade, 
and the value changes also according to the position of the observer 
with regard to the direction of the rays of the sun. In general, the 
Crimean wheats have dark-green blades, while all durum varieties 
have blades with a light-green color. 
The blade widths are mentioned in describing only a few varieties, 
because nearly all varieties are very much alike in this character. 
The Crimean wheats are distinctly narrow leaved, while varieties 
like Sol and Red Russian have wide leaf blades. In America the 
winter varieties having the narrowest blades usually are most winter 
hardy. The length of the blade has not shown sufficient constant 
differences for taxonomic purposes. 
The terminal leaf of different varieties of wheat is sometimes quite 
erect and sometimes drooping at various angles. These differences 
are greatest just previous to the heading period, but frequently are 
not apparent a few days later. Chiefly because of the instability of 
this character, it is not used in this classification. 
The sheaths normally inclose about the lower two-thirds of the 
culm, although in dry seasons the spike sometimes is not entirely 
