350 MR. L. LEWTON-BRAIN ON THE ANATOMY 
low rounded ribs. The ribs are most prominent in Festuca bromoides; in the great 
majority of cases they are practically obsolete. 
As in the meadow-grasses, stomata usually occur on both sides of the leaf, and 
generally they are more abundant on the upperside. Again, the cells of the lower 
epidermis are very often more strongly cutinized than those of the upper, though usually 
the difference is not a very marked one. These differences are fairly well marked in 
Festuca Myuros and F. bromoides, but certainly not more so than in F. duriuscula among 
pasture-grasses. 
A certain number of the leaves are very hairy (Pl. 39. fig. 43; Pl. 37. fig. 27), and this 
may be regarded as a protection against excessive transpiration, also perhaps against 
the smothering of the leaves with dust. But this feature is by no means a general one, 
and is, in fact, hardly more common here than in the meadow-grasses. 
As in meadow-grasses, again, the leaf is usually not markedly broad or narrow, thick 
or thin. The stereome is arranged, as in meadow-grasses, in bands or girders above and 
below the vascular bundles, and it is, generally speaking, neither more nor less abundant 
than in pasture-grasses. In Festuca Mywros the stereome is not abundant, and it is 
confined to the lower side of the leaf; this indicates a slight transition to the heath- 
grass “type” of leaf, but it is not more marked than in F. duriuscula. 
Certain grasses of this group show various exceptional features in their leaf-structure 
. which may perhaps be mentioned here. 
Setaria viridis certainly possesses the most exceptional leaf-structure of all the grasses 
I have examined. The enormous epidermal cells and the great number of small vascular 
bundles are both features peculiar to this grass; the small amount of stereome is also 
exceptional, while the arrangement of the chlorophyll-cells in rings around the bundles 
is met with in only a few other British grasses; the last feature, as has been noted 
above, is probably a xerophilous character. 
Poa rigida also possesses this peculiar type of chlorophyll-tissue. 
Aira precor and A. caryophyllea are noteworthy on account of the extreme smallness 
of their leaves; they both inhabit very dry situations, and this smallness of the leaf is in 
itself a xerophilous adaptation, rendering any change in the leaf-structure unnecessary. 
The leaf-sections may perhaps be described as of a reduced type of that of a heath- 
grass. The general feebleness of the tissues is directly dependent upon the reduced size 
of the leaf. 
ii. Grasses of Woods and Shaded Places. 
Grass. Duration. Figure. 
Melica uniflora . Perennial. 32 
— nutans . — 
Bromus asper . Annual ys 26 
Perennial. 
giganteus . Perennial. — 
Poa nemoralis oe 4 WOW QN v.d " — 
me eju o . . vo. Iw NTXCESN s 35 
HI 
Brachypodium sylvaticum . . . . . 
oe 
