66 HAIRS AND ASPERITIES [CH. 



between and above the veins, but in Hierochloe &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 pratemis, Arundo PfiragmiteSy 



Arrhenatherum avenaceum, Glyceria Jluitans. 



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 Kceleria 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. Each 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. 



