998 . MR. L. LEWTON-BRAIN ON THE ANATOMY 
both surfaces. Motor cells very conspicuous. Bundles of three orders, the larger ones 
contain a large number of fibres and have an exceedingly strong inner sheath; these 
points are less marked towards the margin of the leaf. Stereome very strong; it forms 
girders to most of bundles, also a subepidermal band in midrib. Chlorophyll-cells 
polygonal, small and closely packed. 
[Not a typical heath-grass nor a typical aquatic grass, but the leaf-structure shows features which are 
characteristic of both groups. | 
§§ No conspicuous air-cavities in mesophyll. 
HiEROCHLOÉ BOREALIS (Pl. 38. fig. 30). Royal Botanic Garden, Edinburgh. May 1901. 
Lower epidermal cells flat and well cutinized, those of upper epidermis less so. Motor 
cells very conspicuous. Bundles mostly large. Stereome strong, forming girders to 
large bundles and bands below smaller ones. 
AGROPYRUM REPENS. Cambridge. July 1900. 
Lower epidermal cells rather more strongly cutinized than upper, neither very strong 
nor flat. Bundles numerous, of three orders. Three bundles in midrib, one in each of 
other ribs. All have both sheaths, though not always, marked. Stereome abundant; 
girders to the larger bundles; other bundles may be girdered or have bands above and 
below or none. : 
HORDEUM MURINUM. Cambridge. July 1900. 
Neither epidermis strongly cutinized. Short sharp hairs, more numerous above. 
Bundles three in midrib, one in each of the other ribs. Larger bundles girdered, at 
least below; no stereome in connection with smaller bundles. All bundles have both 
sheaths, though they are not conspicuous. 
[As regards the genus Hordeum, we should not perhaps expect to find any marked difference in leaf- 
structure between H. pratense and H. murinum, one being found in meadows, the other in waste places; 
and there certainly are no differences that can be regarded as due to the influence of the environment. 
The chief difference between the two leaves is the prominent midrib of H. murinum, that of H. pratense 
not projecting below and not being in any way marked off from the other ribs. H. pratense is more 
hairy than H. murinum, but this is a character liable to variation ; also the former possesses more abundant 
stereome. Moreover, when we consider the stunted habit of H. maritimum, especially the small size of 
the leaves, and its short period of vegetation, we should not expect it to possess markedly different leaf- 
structure, in spite of its more xerophilous habitat. This we find to be the case, its leaf-structure being 
feeb er than that of the other two species, and in no way showing any modification in the direction of 
greater xerophily, but rather the reverse.] 
BROMUS GIGANTEUS. Cambridge. July 1900. 
Cells of lower epidermis slightly more strongly cutinized and flatter than those of 
upper. Somewhat sparse, short, stiff hairs above only. Bundles of three orders; all 
have both sheaths, but the cells of inner one are not very thick-walled. Larger bundles 
girdered at least to lower side, others have bands of stereome above and below, or below 
or above, or none. 
[This grass is sometimes included in the genus Festuca ; the leaf-structure differs from that of any 
species of Festuca, but resembles closely that of the other species of Bromus. 
