v] LEAF-STRUCTURE 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: sclerenchyma 
below in a continuous band. 
Atra flecuosu. 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). 
©© 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 
