16 BULLETIN 1386, tJ. Sv DEPARTMENT OF AGRICULTURE 
showing differentiation, in many cases very pronounced, make them 
of value. The fact that each panicle contains a number of spikelets 
also makes it possible to substantiate the characters with much cer- 
taint}'. Hackel (8, pp. 499-520) made use of form of spikelet and 
texture of the glumes as major characters for distinguishing his 
groups; Pech (12) and Collier (5) employed certain spikelet char- 
acters in their keys, particularly the relative length of the glumes 
and caryopsis, which they used as means of separating major classes; 
Ball (2) also employed certain spikelet characters in distinguishing 
between groups and between varieties. 
SIZE OF THE 8PIKELETS 
The length of the spikelets in varieties examined ranges from 0.1 
to 0.25 inch. There is much less variation in size within panicles and 
within varieties than there is in the length of branches of the panicle 
of either primary or secondary rank, the average length in the 
variety which has the shortest spikelets being approximately 0.12 
inch and approximately 0.22 inch in the one in which the spikelet 
length is greatest, these varieties each showing the same ranges of 
spikelet lengths and the same average lengths in spikelets for the 
years 1920, 1922, and 1923, in which this character was examined. 
Although their size is possibly sometimes slightly affected by en- 
vironmental influences, it is without doubt always less so than is that 
of the panicle itself or its branches. Because differences between 
some varieties are very large, the character is useful. The relative 
length of glumes and caryopsis is discussed in a subsequent paragraph. 
FORM OF THE SPIKELETS 
In regard to form, the spikelets of the varieties in general may be 
considered as belonging to one of three groups — the ovate, the 
elliptic, or the obovate, these terms referring to the outline of the 
spikelet as viewed dorsally or upon the dorsal surface of one of the 
glumes, not taking into consideration the caryopsis. which is fre- 
quently more or less exserted from the glumes. Although the first 
glume is inserted below the second and commonly is partially 
wrapped around it even in the mature panicle, the outline presented 
by the two glumes is usually approximately the same. Occasionally, 
however, there is a slight difference, and the first glume usually best 
indicates the form of the spikelet. Its outline, being somewhat 
larger than that of the second, usually forms the outline of the 
spikelet. The terms " ovate," " elliptic," and " obovate " are used in 
a general sense to indicate forms whose greatest breadth is below the 
middle points in its length, at the middle, and above the middle, 
respectively. These three primary forms of spikelet are shown in 
Plate XI and Plate XII, C. In a restricted sense these terms, of 
course, have a more definite meaning. There are also intermediate 
forms and fluctuations are often such that forms more or less inter- 
mediate occur in the same panicles with those more distinct and more 
definitely recognizable. In making a key for identification, how- 
ever, varieties may be classified in one of the above groups by taking 
