30 BULLETIN 1074, U. S. DEPARTMENT OF AGRICULTURE. 



exceed 5 cm. in length. From a genetic standpoint there probably 

 are at least three distinct kinds of awnlessness. For the present 

 classification, however, they are all classed as awnless, but in the 

 descriptions the average extreme lengths of the apical awns are 

 recorded. 



Awned varieties are those that have an awn or beard which termi- 

 nates the lemmas on all spikelets. These awns usually increase in 

 length from the basal part of the spike upward. In the common 

 wheats, awns seldom, if ever, exceed 10 cm. in length. In durum and 

 poulard wheats, however, they usually range from 10 to 20 cm. in 

 length. 



SHAPE OF THE SPIKE. 



Spikes differ greatly in shape, length, and width. They may be 

 flattened parallel to or at right angles to the plane of the face of the 

 spikelets. Those flattened parallel to this plane are widest when seen 

 in face view and can be said to be dorsoventrally compressed. All 

 varieties of common wheat have spikes thus formed, except those 

 that are clubbed at the tip, in which case they are only partly so. 

 Spikes that are flattened at right angles to the plane of the face of 

 the spikelets are narrow when seen in face view and may be described 

 as laterally compressed. The club, durum, and poulard wheats are 

 separated from the common wheats partly on the basis of having 

 such spikes. 



In general, spikes vary in length from 5 to 15 cm., but are usually 

 8 to 12 cm. long. They vary in width or thickness from 1 to 3 cm. 

 The differences in length and width are not used in themselves but 

 are often combined with the spike shape in a compound descriptive 

 word. 



Whether dorsoventrally or laterally compressed, whether long or 

 short, or narrow or wide, spikes are classified in the keys as having 

 the following four general shapes — fusiform, oblong, clavate, and 

 elliptical. These shapes are shown in Plate V. For all common 

 wheats these shapes are determined from a face view of the spikelets 

 and for all club, durum, and poulard wheats from an edge view of 

 the spikelets. 



Heuze {112) used several different spike shapes as the leading 

 characters in separating varieties within the species. The shapes 

 mentioned, however, are here considered only as minor characters, 

 though nevertheless very useful in distinguishing varieties. 



Spikes classed as fusiform taper toward the apex or from the 

 middle toward both base and apex. The larger number of varieties 

 of common wheat have spikes of this shape. 



Spikes described as oblong are usually quite uniform in width 

 and thickness throughout the length of the spike, but are always 

 several times longer than wide. 



