66 HAIRS AND ASPERITIES [CH. 
between and above the veins, but in Hverochloe &c. they 
are confined to the margins. 
The following grasses have no hairs of either type: 
Agrostis vulgaris, Dactylis glomerata, 
Calamagrostis lanceolata, Briza media, 
Avena pratensis, Arundo Phragmites, 
Arrhenatherum avenaceum, Glyceria fluitans. 
The sharp, hard prickle-hairs which give the pro- 
nounced roughness to many leaves of grasses are longer 
than the foregoing, and stand off more from the leaf. 
They occur both on the surface and at the margins, and 
may be isolated—e.g. Avena pratensis——or mixed with 
the short cells—Aira canescens, Elymus arenarius. They 
are very abundant on Keleria cristata. . 
Leersia oryzoides has asperities at the margin of the 
leaf with their points directed upwards on the upper part 
of the leaf, downwards on the basal parts, and the direction 
Fig. 24. Transverse section of part of leaf of Agropyrum junceum 
(x about 40) partly inrolled; showing unequal ridges. The principal 
vascular bundles are girdered below, the sclerenchyma joining into a 
strong continuous sheath. Lach ridge is tipped with sclerenchyma, 
and each groove has motor-cells—not shown in the figure—below. 
of such minute marginal asperities often affords a useful 
distinctive character—e.g. Phleum, Arrhenatherum. The 
marginal asperities in Nardus are siliceous. 
