18 



SHEATH AND LIGULE 



[CH. 



prominent ridge down its back, due to the continuation of 

 the heel 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 coloui*ed. 



Lolium — all red. 

 Uolcus — red with purple veins. 

 Festuca elatior — red. 

 Cynosums — yellow. 

 Alopecurus pratensis^ and 

 A. agrestis — violet-brown, &c. 

 FestiiAia ovina^ var. riibra — red- 



Eig. 8. Poa trlvialis. 



A, base of blade. 



B, Ugule. C, 

 sheath. D, culm 

 ( X about 3). 



Fig. 9. Alopecurus 

 pratensis. ^,base 

 of blade. Bjligule. 

 C, sheath. Slight- 

 ly magnified. 



Fig. 10. Arena Jiavescens. 

 Lettering as before 

 ( X 2). Note the split 

 sheath, the hairs and 

 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 



