290 



MONOCOTYL EDONES. 



rolled up and almost filiform or bristle-like, with anomalous anatomical 

 structure. A closed tubular sheath is found in Melica uniflora, Bromus -species, 

 Poa pratensis and trivialis, Briza and some GZ?/cm"a-species. The sheath is 

 developed for the purpose of supporting the young internodes while their growth 

 is proceeding at the base. The " nodes " (the swollen joints which are seen on 

 stems of Grasses) are not really part of the stem but are formed by the base of 

 the leaf-sheath. They play a part in assisting the haulms to regain a vertical 

 position when laid prostrate by wind or rain. The awn on the pale is homo- 

 logous with the blade of the Grass-leaf, and the pale itself is the sheath. The 

 arrangement of the leaves in the spikelet is similar to that in Ci/perus and other 

 Cyperaceae, their floral-leaves being borne in several rows in Streptochceta. More 

 than two barren "glumes" are found in Streptochcsta, several Phalarideae and 

 others. The spikelets, too, are again arranged in two rows in the axils of sup- 

 pressed floral-leaves. The inflorescence becomes a " compound spike " (ear; when 



FIG. 290. Diagram of the Grass-flower .- 

 ni outer pale ; 0i inner pale ; l-I lodi- 

 cules. 



FIG. 291. Longitudinal section of an 

 Oat-grain .- a the skin (pericarp and 

 testa); b the endosperm; c the cotyledon; 

 d the plumule. 



the spikelets are sessile. In the majority of instances the spikelets are borne 

 on long stalks ; when these branch, then the secondary branches, and similarly 

 all branches of higher order, are placed so far down upon the mother-axis that 

 they all appear to be of equal value and to arise in a semicircle from the mother- 

 axis itself, though in reality they arise from each other (Panicle, Fig. 288 A). 

 Sometimes the main axis and branches of different orders unite together as in 

 Alipecurus, Phleum, and some other Grasses, and hence the single (short- 

 stalked) spikelets appear to arise singly and spirally, or without any definite 

 order, directly from the main axis, with the production of a cylindrical inflor- 

 escence bearing "spikes" on all sides, that is, a "spike-like panicle." Many 

 inflorescences are somewhat dorsiventral. The flower is rarely unisexual (Zea 

 mc.is) or barren. Considerable difficulty is experienced in reducing the Grass- 



