Fig. 12.—Prophylla.
A. A branch with its prophyllum; B. prophyllum; C. section of the prophyllum.
The ordinary foliage leaves of grasses consist of the two parts, the flat expanded upper portion called the blade and the lower part called the sheath that encircles the stem above the node from which it arises. The leaf-sheaths usually fit close to the stem, but they may also be loose or even inflated. Though the leaf-sheath surrounds the internode like a tube, it is not a closed tube. It is really a flat structure rolled firmly round the stem with one edge overlapping the other. In most cases it is cylindrical and it may be compressed in a few cases. Occasionally it may have a prominent ridge or keel down its back. The sheath may be glabrous or hairy, smooth or striate externally, and the outer margin is often ciliate. In a few grasses the sheaths become coloured especially below or on the side exposed to the sun.
Fig. 13.—Ligules of 1. Oryza sativa; 2. Panicum javanicum; 3. Andropogon Schœnanthus; 4. A. contortus.
