_Poa maritima_, Huds. (Sea-grass). Leaves narrow, rather short, and U-shaped in section. Involute: ridgeless, with flanking lines, but no keel; soft and rather thick. Ligule rather long, obtuse and decurrent. Useless agriculturally. For difficulties with other species of _Avena_ and _Poa_ see pp. 44, 54 and 60. (_b_) Grasses with the leaves expanded, more or less flat. (1) Blades conspicuously ridged--i.e. the surface is raised in prominent longitudinal ridges with furrows between. (i) _Leaves rigid and hard, sharp pointed. Sheath and outer leaf-surface usually glabrous._ _Aira cæspitosa_, L. (Tufted Hair-grass). Forms large tufts. A coarse weed forming bad tussocks in wet meadows and pastures: useless for fodder. Leaves flat. Ligule long, acute. Ridges equal, high and sharp, and scabrid, with 5-6 white lines between, if viewed by transmitted light. Wet meadows. _A. cæspitosa_ cannot easily be mistaken for any other species. _Alopecurus geniculatus_ is also a moisture-loving grass with strongly ridged leaves, but the interspaces are far less translucent and the whole habit is different. All the other species of _Aira_ have involute and setaceous leaves, and even _A. cæspitosa_ is apt to roll in its leaves in mountain varieties, but they are easily flattened out, and show the ridges. _Psamma arenaria_, Beauv. (Sea Mat-grass). This is one of the most valuable “sand-binders,” its long matted rhizomes holding loose sand together. It is a sea-shore grass, of no use for fodder. It was formerly much used for mats and thatching. Leaves concave, long, narrow, erect, scabrid and glaucous above, and polished below: pungent. Ridges rounded, alternately high and low. Sheath long. Ligule very long and bifid. _Elymus arenarius_, L. (Sand Lyme-grass). Like _Psamma_, this is a “sand-binder” and of no use for fodder. Leaves concave, and eared at the base of the blade: ears pointed and tend to cross in front. Ligule very short and obtuse. Ridges flattened above, not scabrid. Apex of blade rolled, forming a hard spine. _Psamma_ cannot easily be mistaken for the much less common _Elymus_, as it is not eared, and the ridges and ligule are very different. (ii) _Leaves not specially rigid and hard, and often thin; glabrous, or shining below. Ridges less evident._ * _Ligule very short or obsolete; blade firm but not hard, glabrous or nearly so, and shining below. Sheath often coloured red or yellow at the base._ † _Sections of sheathed leaves narrow, oblong, owing to compression of shoots. Sheath nearly entire._