332 MR. L. LEWTON-BRAIN ON THE ANATOMY 
arrangement of the stereome, chiefly in broad bands under the lower epidermis, depends upon the 
narrowness of the leaf and the fact that this is generally folded. 
The remaining species show very clearly a gradual change from the meadow-grass to the heath-grass 
type of leaf-structure. In Festuca duriuscula, which is characteristic of drier pastures than F. elatior and 
F. pratensis, we find a smaller number of ribs, which are covered with hairs ; of these the midrib is the 
largest, though not conspieuously so ; we find also the lower epidermal cells strongly cutinized and with 
flat outer surfaces, and that the stomata are confined to the upperside of the leaf; these changes are all 
in the direction of greater xerophily ; again, we find that the stereome, which is much smaller in amount 
owing probably to the smaller size of the leaf, is practically confined to the lower side. "The lower flat 
leaves of F. rubra are very similar in structure to those of F, duriuscula, the chief difference being the 
shorter hairs and the presence of a fair amount of stereome on the upperside. "The upper subulate 
leaves, however, show a distinct advance; the midrib is relatively much more prominent, and there are 
only four other ribs. In some specimens of F. ovina (Pl. 96. fig. 3) we get a very similar leaf-structure 
to that just mentioned, only the midrib is relatively even more prominent and there is no stereome on 
the upperside. In other specimens of the same species (fig. 4) the type is even higher; there are only 
two ribs besides the midrib, and the stereome forms an almost continuous subepidermal band. We have 
thus arrived by easy stages at what is a quite typical leaf-structure for a heath-grass. | 
$$ Hairs long and numerous. 
|| Stomata on upperside only. 
FxsTUCA DURIUSCULA (Pl. 87. fig. 17). Kinghorn, Fife. May 1901. 
Rather few but well-marked ribs on upperside. Abundant, fairly long, strong hairs 
on upperside. Vascular bundles few, of two orders. Stereome in small bands, mostly 
on lower side. Larger bundles have strong inner sheaths. 
UI A few stomata below also, as a rule. 
Festuca Myvros. (See p. 331, above.) 
i. Hairs inconspicuous or none. Cutinization of epidermal cells usually moderate or feeble, that 
of the lower surface the stronger. 
* Asperities or sparse short hairs, chiefly above. 
t Stereome forming girders to some or all vascular bundles. 
t Motor-cell groups conspicuous in all the grooves. 
$ Stomata fairly numerows on both surfaces. 
ALOPECURUS PRATENSIS (Pl. 37. fig. 18). Swanton Morley, Norfolk. June 1901. 
Ribs of two orders, both rounded. Stereome fairly abundant, many bundles girdered 
tolower side and with bands above; bands also above and below, or only below other 
bundles. 
Kinghorn, Fife. May 1901. 
Exactly as above. 
Royal Botanic Garden, Edinburgh. May 1901. 
Same, but some of central grooves have disappeared. 
