26 KEELED AND HAIRY 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 less prominent. 
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 
pubescens, 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 cerulea. Anthoranthum. 
Brachypodium sylvaticum. Avena flavescens (Fig. 10). 
Agropyrum (variable). A, pubescens. 
Bromus asper. Triodia. 
B. mollis. Keleria. 
To a less extent. 
Festuca sciuroides (on ribs). Melica. 
