104 A TEXT-BOOK OF GRASSES 
130. Leaf-base and blade.—As regards development, 
the leaves of flowering plants consist of two portions— 
the leaf-base and the blade. The leaf-base is prominent 
in the early development of the organ, but generally 
includes only a small portion of the mature leaf. In the 
leaves of common deciduous forest trees, the swollen 
portion at the base of the petiole represents the leaf-base. 
In reduced leaves, the leaf-base often includes a relatively 
greater portion or may even be the only portion developed. 
In grasses, the sheath represents the leaf-base. In scales 
and bracts, the blades have failed to develop or consist 
~ of a mere tip or point. 
131. The prophyllum.—At the point where a branch 
shoot originates from a main shoot, there is produced on 
the side next to the parent shoot a 2-keeled organ called 
the prophyllum. Through pressure the back of the 
prophyllum between the keels is concave against the 
parent shoot, while the two lateral portions, outside the 
keels, bend forward clasping the new shoot. At first the 
prophyllum completely covers the young shoot or bud, 
but later is spread or opened as the shoot develops. 
The various subdivisions of the leaf will now be dis- 
cussed more in detail. 
132. The sheath is the lower portion of the leaf that 
encircles the culm above the node from which it arises. 
From the developmental standpoint it represents the 
leaf-base. The sheath is usually open from the base on the 
side opposite the blade, the right and left margins of suc- 
cessive sheaths overlapping alternately. 
The sheath usually fits close to the stem but may be 
loose or inflated, especially the uppermost. The old sheaths 
at the base of the shoots may persist in perennial grasses 
and assume a characteristic appearance. 
