16 THE SEEDS OF THE BLUEGRASSES. 
The caryopsis corresponds to an individual grain in wheat, rye, and 
barley, and consists almost entirely of the seed proper, to which is 
added only the thin wall of the seed vessel. This is intimately blended 
with the seed coat, the two forming the covering of the true seed. 
The caryopsis is spindle-shaped and often broadest between the middle 
and the base. It is often bluntly keeled along one face and more or 
less evidently grooved along the opposite face. In the: commercial 
bluegrass seeds the grain is amber-colored or dull wine-colored and 
semitranslucent. The surface is finely granular and dull. The kernel 
of the seed forms that part of the grain within the seed and seed- 
vessel walls. It consists of the embryo and endosperm, the latter 
forming the greater part. The embryo is situated at the basal 
extremity of the grain and is evident externally as a small ridge, often 
within a slight depression, on the keeled face. The grain adheres 
along its grooved face to the palea in some species in which free grains 
are not common in well-cleaned commercial seed. 
The two chaffy scales of the floret differ chiefly in size, form, rela- 
tive position, venation, and texture. The larger one, called the flower- 
ing glume or simply the glume, incloses the edges of the other, termed 
palea. The grain rests between the glume and palea, its keeled face 
lying against the glume. The rachilla segment is at the base of the 
palea and opposite the glume. It is one of the articulating sections of 
the rachilla, or axis of the spikelet. 
The characters by which the different kinds of bluegrass seeds are 
distinguished one from another are afforded by the glume, palea, and 
rachilla segment, and involve size, form, color, veins of the glume, 
form and texture of the apex of the glume, and the pubescence. 
The glume is stifish and more or less pointed at the ends. Its base 
is marked by the presence of a small, somewhat knob-like appendage, 
the callus. The latter bears the scar of attachment of the floret and, 
in certain species, a more or less pronounced tuft of webby hairs. 
The back of the glume is more or less keeled along its longitudinal 
center. Besides the fold forming the keel, the edges of the glume are 
infolded along the marginal veins. ‘The marginal folds often are most 
pronounced within and sometimes are confined to the lower half of the 
glume, in which event the upper margins usually diverge and become 
spreading or flaring at the apex. The keel is strongly arched length- 
wise in some species and in others is nearly straight. Five veins 
traverse the glume longitudinally; one occupies the keel, two are at 
the marginal folds and are termed the marginal veins, while the other 
two are situated midway between the keel and marginal veins and are 
called intermediate or, by some authors, lateral veins. The interme- 
diate veins exhibit considerable variation in distinctness in the differ- 
ent species. The vein occupying the keel extends to the apex. The 
apex and often the upper part of the lateral margins of the glume in 
