26 KEELED AND HAIKY GRASSES [CH. 



In some grasses the tissue over the mid- rib is con- 

 siderably raised and strengthened on the dorsal side of the 

 blade as a " keel." 



Keel more or leas promiiient. 



Arrhenatherum (sheath keeled). 



Poa (all except P. maritima). 



Dactylis. 



Bromus. 



Bromus asper (sheath keeled, often a white line). 



Holcus lanatus (slight and decurrent) (Fig. 15). 



Digraphis (Fig. 14). 



Glyceria. 



Most grasses are glabrous, but there are a number in 

 which hairs are nearly always a prominent feature. It 

 must be remarked, however, that with grasses, as with 

 other plants, the character of pubescence is apt to vary 

 with the situation. In general it may be stated that a 

 hairy grass tends to become more glabrous in a moist 

 situation, and more pubescent in a dry one, but the rule 

 is by no means absolute. In some cases, — e.g. Avena 

 puhescens, A. flavescens, Agropyrum, the hairs are almost 

 entirely confined to the crests of the ridges (Figs. 10, 15). 

 The following is a list of hairy grasses. 



Hairy Grasses. 



Holcus (Fig. 15). Hordeum. 



Molinia ccerulea. Anthoxanthum. 



Brachypodium sylvaticum. Avena Jlavescens (Fig. 10). 



Agropyrum (variable). A. puhescem. 



Bromus asper. THodia. 



B. mollis. Kceleria. 



To a less extent. 

 Festuca scmroides (on ribs). Melica. 



