352 MR. L. LEWTON-BRAIN ON THE ANATOMY 
iv. Grasses of Maritime Sands. 
Grass. Duration. Figure. 
Festuca elatior, var. arundinacea. . . . . . Perennial, 11 
Hordeum maritimum. . . . . . . »- . . Annual. 16 
Cynosurus echinatus 2. . + + e © © + A 51 
Agropyrum junceum =. a s . >o ++ + + « Perennial. 13 
Tar ea . «9. 4 RR En € e 12 
een EE, «. Anaal. I 
lege geen, e Perennial, 9, 14 
Somas mummud V a eee ee Annual. 41 
Pos JEEP CS LM i en Porennial. 47 
Te E AS aa Annos. — 
atin MINE ac RE e r i = 
Deeg e SE e cher a O e Sh 8 
Among all these grasses the leaf-structure can only be described as “typical” in three 
— Psamma arenaria, Agropyrum junceum, and Elymus arenarius (Pl. 36. figs. 9, 12, 18, 
14); of these Psamma arenaria shows the most highly specialized leaf-structure. 
The habitat of these grasses is pronouncedly xerophytie; the water-supply is small 
and very variable, while the conditions are extremely favourable to rapid transpiration. 
Moreover, the leaves, and especially the large ones, are often subjected to great 
mechanical strain. 
Corresponding to this we find the leaf-structure of the three grasses mentioned to be 
of a strongly xerophilous type. 
The leaf is broad, thick, and hard in consistency: the upperside is provided with 
high well-marked ribs; in Psamma arenaria and in Agropyrum junceum the ribs are 
covered with numerous rather short hairs. The stomata are confined to the flanks of 
the ridges, where they are well shut in and are, moreover, further protected by the hairs. 
Again, the cells of the lower epidermis are very strongly cutinized and their outer 
surfaces are quite flat; the cells of the upper epidermis are quite strongly cutinized, 
though not so strongly as those of the lower. "These features, then, secure in the first 
place the complete restriction of the transpiring surface to the flanks of the ridges, and 
in the second place the protection of this restricted area by sheltering the stomata from 
air-currents. The groups of motor cells at the bottom of the grooves are not at all 
conspicuous; we cannot, therefore, judge of the activity of these cells by their 
prominence in sections. 
The vascular bundles are large and possess conspicuous inner and outer sheaths ; the 
inner sheath is particularly well marked in the larger bundles. "The bundles are probably 
capable of conducting large supplies of water after rains. 
The stereome is extremely strong and abundant, the bundles are strongly girdered at 
least to the lower side, and in Psamma arenaria and Agropyrum junceum we get a strong 
subepidermal layer of stereome on the lower side of the leaf; this is not met with in the 
leaf of Elymus arenarius, except just at the tip. The amount and arrangement of the 
stereome can, I think, as I have shown above, be explained on purely mechanical 
grounds, 
