342 MR. L. LEWTON-BRAIN ON THE ANATOMY 
«« Surfaces quite smooth. 
PoA ALPINA, var. VIVIPARA. Ben Lawers. July 1901. 
Agrees with description of P. alpina (see p. 340), except that there is rather less 
stereome and no bundles are girdered. 
Poa ANNUA. Cambridge. July 1900. ` 
Leaf rather thin. Cells of epidermis arched. Stomata few on both sides. Sheaths 
not well marked. Stereome-bands above and below or only below to bundles. 
$$ Motor-cell groups inconspicuous. Surfaces slightly papillose. Air-chambers in 
tissue. Stomata about equal both sides. 
GLYCERIA FLUITANS (Pl. 38. fig. 39). Swanton Morley, Norfolk. June 1901. 
Epidermal cells on both sides mostly raised into papillee. Vascular bundles large and 
numerous, between the ridges. Stereome feeble, bands above and below bundles. 
Fairly large air-laeunze between bundles. Bands of thin-walled colourless cells join 
bundles to stereome. 
Linlithgow. June 1901. 
Ridges less marked. Motor cells more conspicuous. Otherwise as above. 
[ With the same habitat, it is to be expected that the two species of Glyceria should have a similar leaf- 
structure, and it will be seen that these two grasses have one of the most characteristic leaf-structures 
among British aquatic grasses. The larger air-lacune of G. aquatica are probably dependent upon the 
larger size of the plant, and the stronger cutinization of the epidermal cells is probably due to the same 
cause, as the leaves are thereby more exposed to the wind. The low ribs of G. fluitans are harder to 
explain, they probably have no significance as an adaptive character. | 
6. Midrib obsolete, or at least not prominent as a keel below. Stomata on both sides. 
i. Hairs conspicuous in number or length, or both. 
* Stereome relatively abundant, and forming girders to some or all vascular bundles. Motor 
cells between all ribs. Cutinization usually moderate. 
T Motor-cell groups conspicuous. Stomata more numerous above. 
1 Hairs very numerous, rather short and sharp, on upper surface only. 
HORDEUM PRATENSE (Pl. 38. fig. 40). Madingley Road, Cambs. August 1900. 
Cells of lower epidermis fairly strongly cutinized and flat, those of upper less so. 
Stomata much more abundant above. Bundles all have both sheaths, but in those of 
third order the inner sheath is not conspicuous. Bundles nearly all girdered, some only 
to lower side, and with bands of stereome above. 
27 Hairs long, stiff, and fairly numerous both sides. 
Bromus MAXIMUS (Pl. 39. fig. 41). Royal Botanic Garden, Edinburgh. June 1901. 
Cells of epidermis arched. Both sheaths fairly conspicuous. Stereome fairly abun- 
dant; some bundles are girdered on both sides, others have bands on both or on one 
side only, others have no bands above or below. 
