V] LEAF-STRUCTUEE 79 



Psamma arenaria. Inrolled. Smooth below and devoid 

 of keel, with sub-epidermal band of sclerenchyma, and 

 similar tissue at the margin. Ridges of three sizes, the 

 largest twice or three times as high as the leaf-tissue 

 between is thick, all rounded above, and very hairy. 

 Stomata above only. Motor-cells in each sinus not large. 

 Vascular bundles isolated, without girders or bands of 

 sclerenchyma. 



Elymus is very like Psamma, but has a few stomata 

 below and the sub-epidermal sclerenchyma is not con- 

 tinuous (see Fig. 25). 



** Leaves {subulate) not opening out, the upper surface 

 represented by a groove or a few ridges above the 

 angular or ovate solid section. 



© Section pentagonal or angular-ovate: scleremchyma 

 below in a continuous band. 



Aira flexuosa. Upper surface a depression, with one 

 ridge flanked by two grooves at its base, the depression 

 extending about one-fifth through the whole thickness 

 of the nearly solid leaf. Vascular bundles about 3 — 5, 

 isolated, sheathed. Sclerenchyma band extending all 

 round the lower surface just inside the thick cuticle. 

 Stomata very few, flanking the ridge ; motor-cells in the 

 furrows, poorly developed (Fig. 28). 



©0 Section elliptical or angular-ovate; sclerenchyma 

 not always in a continuous band below. 



Festuca ovina. Upper surface a deep fold, with three 

 ridges and 2 — 4 grooves at its base. Vascular bundles 

 several, with girders. Motor-cells in four series, in the 



