The permanence and character of extensive grasslands, especially prairies, savannahs, and steppes, are much affected by the periodical firing they are exposed to in the dry season, and large tracts of country in various parts of the world would doubtless bear forests or other vegetation if not thus fired, while in other cases the herbage would be differently constituted were firing discontinued. The following chapter embodies an attempt to classify our British grasses solely for purposes of identification when not in flower. It is not claimed that the arrangement is the best possible, nor that it is complete, and I need hardly say that corrections will be gratefully received. CHAPTER III. GRASSES CLASSIFIED ACCORDING TO THEIR VEGETATIVE CHARACTERS. I. SHEATHS ENTIRE EXCEPT WHERE THOSE OF LOWER LEAVES ARE BURST BY BRANCHES, &C. +A. Aquatics with the sheaths reticulated, owing to large air-cavities. Leaves equitant, linear acute, often floating.+ _Glyceria fluitans_ (Br.). Floating sweet grass. Somewhat coarse, but useful pasture in water-meadows and fens. Sweet-tasting. Section of sheathed leaves linear oblong; sheath striate or furrowed, keeled; leaf ribbed; ligule broad acute. Leaf-base with a yellow triangle. Smooth. _Glyceria aquatica_ (Sm.). Reed sweet grass. Especially given to growing in the water-courses and on banks instead of spreading in the water-meadows, &c. Sweet-tasting. Section of sheathed leaves broadly naviculate; sheath smooth, no keel; leaf not ribbed, thick and inflated with large air-cavities; ligule short. Leaf-base with a brown triangle. Margins and keel rather rough. These two species of _Glyceria_ are distinguished by their shoot-sections and the ridges of the leaves of _G. fluitans_: they often occur in the same ditch. They cannot readily be confused with others on account of their aquatic habit, and the characters given. The only other aquatic or semi-aquatic species are forms of _Catabrosa_, _Digraphis_, _Arundo_, _Alopecurus geniculatus_, _Molinia cærulea_ and the rare _Calamagrostis_. The ligule and flat shoots with closed sheaths alone suffice to distinguish it from the round and split sheathed _Arundo Phragmites_; and the round shoots of _Digraphis_, its split sheath and firm leaves, suffice to distinguish it. _Molinia_ also has a tuft of hairs instead of a ligule, and a split sheath, and its habit is different. _Alopecurus geniculatus_, with its “kneed” shoots, has a totally different habit from _Glyceria_, and its very high ridges and want of visible air-chambers complete the diagnosis. _Catabrosa_ is a small creeping aquatic with very flaccid leaves, quite glabrous and soft. Also sweet-tasting. +B. Not aquatic, and devoid of visible air-chambers in leaf or sheath. Often perennial, i.e. having stolons or other branches with no rudiments of flowers in them, and with relics of old leaf-bases.+