346 MR. L. LEWTON-BRAIN ON THE ANATOMY 
regarded as an adaptation to its environment. In fact, from the leaf-structure one would almost 
certainly judge Cynosurus echinatus to be adapted to far more favourable conditions as to water-supply 
and transpiration than C. cristatus.] 
$$ Motor-cell groups not shallow and wide. 
PHLEUM ALPINUM (Pl. 39. fig. 52). Royal Botanic Garden, Edinburgh. April 1901. 
Low ribs on upperside, some square, others rounded. Stomata rather more numerous 
above than below. The larger vascular bundles have bands above and below, to which 
they are joined by bands of colourless cells interrupting the chlorophyll-tissue; the 
other bundles may have bands of stereome above or below, or above and below, or none. 
PHLEUM ARENARIUM. Yarmouth, Norfolk. May 1901. 
Ribs low, square, and rounded. Lower side flat. Cells of neither epidermis strongly 
cutinized. Cells not flattened. Stomata abundant on both sides. Vascular bundles 
with conspieuous outer sheath, but in smaller bundles the inner sheath is not marked. 
Girders to larger bundles and small bands above and below smaller ones. Chlorophyll- 
tissue with slight tendency to be arranged in rings. 
[Although we have in the genus Phleum representatives of four ccological groups, the structure of 
the leaf is very constant throughout. Taking the pasture-grass, P. pratense, as our standard for 
comparison, we see that the variety nodosum, which is characteristic of more exposed and sandy 
situations, is practically identical in leaf-structure, the only difference being that it shows a slightly 
greater difference between the upper and lower epidermis in the cutinization of the cells and the 
number of stomata. P. alpinum, again, is very similar in structure, differing only in its rather feebler 
stereome and in its thicker leaf; the latter feature is characteristic of alpine grasses. P. arenarium, 
although a sand-dune grass, has the leaf-structure practically identical with P. pratense, showing in this 
respect no adaptation to its environment.] 
tt Motor cells inconspicuous. 
Briza MEDIA. Swanton Morley, Norfolk. June 1901. 
Upper surface with fairly conspicuous ribs, some higher and rounded, others lower 
and square. Stomata on both sides. Vascular bundles few, larger ones in the lower 
ribs. Stereome-bands above and below bundles. 
Fulbourn, Cambs. July 1900. 
Stereome rather more abundant; midrib and one or two of the larger bundles 
girdered below. Otherwise the same as above. 
