En 
OF THE LEAVES OF BRITISH GRASSES. 353 
Poa bulbosa differs in almost every respect from the typical leaf-structure. Though a 
perennial grass, the green subaerial parts are short-lived, lasting only a few weeks in 
spring, so that the leaves do not have to withstand such strongly xerophilous conditions as 
do those of our types; moreover, the leaves are rather small, short, and narrow—charac- 
teristics which tend to reduce transpiration. However, the cells of the lower epidermis 
are strongly cutinized and the stomata are to a large extent confined to the upperside of 
the leaf. The small amount of stereome is dependent upon the small size of the leaf. 
Festuca arundinacea is to some extent intermediate in leaf-structure between our 
typical maritime grasses and heath-grasses. The well-marked ribs covered with hairs 
and the strong subepidermal stereome are maritime characters. In its narrowness, in 
the absence of girders to the bundles, and in the small amount of stereome in the upper 
half of the leaf, the leaf-section resembles that of a heath-grass. The strong cutinization 
of the lower epidermal cells and their flat outer sides, and the absence of stomata from 
the upperside, are features common to both groups. In every respect, however, the 
leaf-section is of a distinctly xerophilous type. 
Lepturus filiformis is an annual, but its leaf-structure shows marked xerophilous 
characters. These, however, are much more like those met with in the leaves of heath- 
grasses than in those of the typical maritime ones—in fact, the leaf-structure is quite 
that of a typical heath-grass. ‘The increase in size of the midrib relatively to the other 
ribs giving rise to a subulate leaf, the absence of girders to the bundles, and the massing 
of the stereome under the lower epidermis are all characters of heath rather than of 
maritime grasses, though there is rather more stereome than is usual in the heath type 
of leaf. The strong cutinization of the lower epidermal cells, the absence of stomata 
from the lower side, and the hairiness of the upperside are characters common to both 
the heath and the maritime type. The arrangement of the chlorophyll-tissue in rings 
about the bundles is a feature shared with a few other grasses (Setaria viridis, Poa 
rigida), all more or less kerophytic in habitat; and, as explained above, it is probably a 
xerophilous modification. 
Poa loliacea is also an annual. The leaf-structure is more or less of a xerophilous 
character, but not so markedly as that of a typical maritime grass. The chief xerophilous 
features are the cutinization of the epidermal cells, the absence of stomata from the 
lower side of the leaf, and the arrangement of the chlorophyll-tissue in rings round the 
bundles. It departs from the maritime type conspicuously in the small amount of 
stereome present, also in the smaller size of the leaf, the less marked ribs on the upper- 
side, and the feebler cutinization of the cells of the epidermis. Its habitat is not that of 
a typical maritime sand-grass, and perhaps it had better have been placed in Group ii. by 
the side of Poa rigida, to which it is closely allied. 
The remaining grasses of this group are all annuals, and the leaves of none exhibit 
any structural features that can be described as adaptive. 
Mibora verna, as already mentioned, is interesting as showing the most reduced leaf- 
structure among British grasses. This is to be explained by the short vegetative period 
of the plant and the smallness of the leaf, the latter itself being a xerophilous 
character. : i 
