* _No trace of ridges, and the mid-ribs not prominent, but the leaves show median lines flanked by finer ones when held up. Blades thin and narrow. Somewhat keeled._ (i) _Shoots compressed._ _Poa compressa_, L. (Flat-stemmed Meadow-grass). Leaves rather short, more or less glabrous or glaucous, and +V+-shaped at the base; shoots compressed, and naviculate in section. Ligule short and thin. Sheath tends to be closed below. A creeping perennial on commons and waste lands, and of little or no value. _Poa annua_, L. (Annual Meadow-grass). Small annual. Compressed shoots, limp. Leaves linear, pale, sub-acute, thin, often wavy, flat, flaccid, bright green; dull or slightly shining and +V+-shaped in section below. Ligule long, pointed, whitish and clasping the shoot. It is a harmless weed, and since it puts out shoots all the year round, furnishes a certain amount of pasturage. (ii) _Shoots terete or nearly so._ _Poa nemoralis_, L. (Wood Poa). Leaves and sheaths smooth. Blade bright green, thin, often glaucous, linear-narrow, flaccid, acute. Ligule almost obsolete. Section of shoots round. Of little value. _Poa bulbosa_, L. (Bulbous Meadow-grass). Stems bulbous at the base. Ligule long and acute. Leaves very narrow and tapering. Sections of shoot round. Coasts of S. and E. All the Poas, except the aquatic ones (_Glyceria_) and _P. maritima_, have glabrous ribless blades with the median lines, and slight keel. _P. pratensis_, _P. alpina_ and _P. trivialis_ (Fig. 8) have entire sheaths (as have _Glyceria fluitans_, _G. aquatica_ and _P. maritima_), but the others have them split some way down. The leaves of _P. pratensis_ and _P. compressa_ are firmer than the thin leaves of _P. annua_, _P. trivialis_ and _P. nemoralis_. Sheaths flattened in _P. pratensis_, _P. compressa_, _P. annua_, and _P. trivialis_; but rounded in _P. nemoralis_. _Glyceria aquatica_ and _G. fluitans_ have netted sheaths. _Poa annua_ is annual, and _P. bulbosa_ has the bulbous base. _P. maritima_ has involute leaves and no keel, and the rare _P. alpina_ has short rigid keeled mucronate leaves, with tip often inflexed and thickened scabrid edges. The leaves of Avena are apt to appear similar to those of the Poas at first sight, but the former are hairy, and ridged, dry as well as thin, and the peculiar median lines of _Poa_ are wanting. _Poa bulbosa_ has drier leaves than usual, but its leaves are devoid of ridges. ** _Ridges can be detected, but are slight and not distinct. Margins scabrid, at least at the base._ † _Leaves firm, flat, linear, acuminate, not narrowed below. Glabrous. Ligule membranous._