OF THE LEAVES OF BRITISH GRASSES. 339 
Though we have in the genus Bromus representatives of three cecological groups, the differences in 
leaf-structure are very small, so much so that one cannot with certainty identify any one species. The 
abundant hairs of B. sterilis may be regarded as an adaptation to its environment, and similarly with 
the thinness of the leaf of B. asper. The other differences met with in the leaves are liable to variation 
and cannot be considered environmental adaptations.] 
tt Stereome relatively scanty, and at any rate not forming true girders to the vascular 
bundles. 
i Motor cells conspicuous in a single series over the midrib. 
DACTYLIS GLOMERATA (Pl. 38, fig. 31). Swanton Morley, Norfolk. June 1901. 
Midrib rather depressed above; a few blunt asperities. Epidermal cells not strongly 
cutinized. Stomata above and below in about equal numbers. Central bundle not 
girdered, but with a strong band of stereome below ; other large bundles girdered above 
and below, smaller ones have bands of stereome variously arranged. At base of blade 
occur large intercellular spaces appearing between most pairs of bundles, and the 
stereome more abundant. 
Burntisland, Fife. May 1901. 
As above, except that stereome is slightly less abundant. 
tł Motor cells in two or more series. 
§ Motor cells restricted to the flanks of the midrib. 
|| Motor-cell groups conspicuous. 
POA NEMORALIS, var. BALFOURII. Ben Lawers. July 1901. 
Stomata on both sides. Stereome not abundant, it forms bands above and below all 
bundles. 
I|] Motor-cell groups inconspicuous. 
Poa TRIVIALIS. Swanton Morley, Norfolk. June 1901. 
Midrib strongly and other main ribs slightly marked below only.  Upperside has 
short sharp hairs. Bundles of three orders; the largest have both sheaths well marked, 
in smaller the inner one is less conspicuous. Bands of stereome above and below 
bundles. 
Edinburgh. May 1901. : 
No ribs marked below, except midrib. Most bundles are half-girdered at least below. 
Poa PRATENSIS. Ben Ledi. July 1901. 
A very few hairs. Nearly all vascular bundles have the inner sheath well marked. 
Stereome forms girders above and below or only below some bundles, bands above and 
below others. 
§§ Motor cells in inconspicuous shallow groups between all the ribs. Sparse hairs 
above and below. i 
MELICA UNIFLORA (Pl. 38. fig. 32). Royal Botanic Garden, Edinburgh. April 1901. g 
Leaf very thin, with a few ribs below, corresponding to each of larger bundles. Hairs 
few, confined to lines above and below bundles. Vascular bundles few. Stereome not 
well developed, forming bands above and below nearly all bundles. 
9c 
SECOND SERIES.— BOTANY, VOL. VI. 
