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



lish density classes of rather indefinite limits. In this way allow- 

 ance was made for the varying conditions. The density classes were 

 finally fixed as lax, midden se, and dense by determining the number 

 of millimeters occupied by 10 internodes of the rachis measured in 

 the center of the spikes. By this method spikes are classed as lax 

 when 10 internodes occupy from 50 to 75 mm., as middense when 10 

 internodes occupy from % 35 to 60 mm., and as dense when 10 inter- 

 nodes occupy from 20 to 45 mm. The greater number of varieties 

 are included in the middense class, which, according to the above 

 measurements, overlaps both the dense and lax classes by two-fifths 

 of their entire range. 



POSITION OF THE SPIKE. 



The position of the spike at maturity is often distinctly different 

 in different varieties. All spikes are here described as erect, inclined, 

 or nodding. Heuze {112) used essentially these same distinctions 

 in describing his varieties. 



Those varieties described as having erect spikes mature with the 

 spike in an approximately vertical position. The spikes of these 

 varieties seldom, if ever, are inclined more than 15 degrees from the 

 vertical at maturity. Spikes of varieties which are described as 

 inclined usually mature at an angle of approximately 15 to 45 de- 

 grees from the vertical, but sometimes are nearly erect, and under 

 some conditions will become slightly nodding. The majority of 

 wheat varieties come within this class. Varieties which are described 

 as having nodding spikes usually mature with the spike in a droop- 

 ing position, the apex of the spike being lower than the base. Spikes 

 of such varieties sometimes are only inclined if they are not well 

 filled with grain when ripe. 



GLUME CHARACTERS. 



The unit of the spike is the spikelet. It consists of several flowers 

 or florets attached alternately to opposite sides of a central axis or 

 rachilla. These flowers, three to five in number, are subtended by 

 two empty scales, called the glumes, the keel of which terminates in 

 a tooth or beak. Each floret consists of a flowering glume, called 

 the lemma, and a thin 2-keeled glume called the palea. These two 

 glumes inclose the sexual organs. The lemma incloses the back, 

 dorsal, or outer portion, of the mature kernel and in the awned va- 

 rieties terminates in an awn. The lemma itself is of little or no 

 use in classification. The palea protects the inner or crease side of 

 the kernel. It differs from the lemmas in having its back, instead of 

 its face, toward the rachilla or axis of the spikelet. Like the 

 lemmas, it is not used in distinguishing varieties. The glumes, how- 

 ever, are much used. 



