18 SHEATH AND LIGULE [CH. 
prominent ridge down its back, due to the continuation of 
the keel of the leaf. The sheath may also be glabrous or 
hairy, and grooved or not. 
A few grasses are so apt to develope characteristic 
colours in their sheaths, especially below, that they may 
often be recognised in winter by this peculiarity. 
Sheaths coloured. 
Lolivm—all red. 
Holcus—red with purple veins. 
Festuca elatior—red. 
Cynosurus—y ellow. 
Alopecurus pratensis, and 
A. agrestis—violet-brown, «ce. 
Festuca ovina, var. rubra—red. 
Fig. 8. Poatrivialis. Fig. 9. Alopecurus Fig.10. Avena flavescens. 
A, base of blade. pratensis. A, base Lettering as before 
B, ligule. (C, of blade. B, ligule. (x2). Note the split 
sheath. D, culm C, sheath. Slight- sheath, the hairs and 
(x about 3). ly magnified. ridges. Stebler. 
At the junction of the blade with the sheath there is in 
most cases a delicate membranous upgrowth of the former, 
more or less appressed to the stem, and called the Ligule 
(Figs. 8—13). Its use is probably to facilitate the shedding 
