This is a floating aquatic grass. Stems are spongy, branching diffusely, 1 foot long, with feathery whorled roots in dense masses at the nodes; branches are short, erect and leafy. The _leaf-sheath_ is smooth, inflated, compressed, with ciliate margins. The _ligule_ is a narrow membrane. _Nodes_ have whorls of roots. The _leaf-blade_ is linear or ovate-lanceolate, obtuse, glabrous, glaucous beneath, base rounded or subcordate, 1 to 3 inches long and 1/2 to 3/4 inch broad. The _inflorescence_ is a panicle, 2 inches long and broad, somewhat triangular in outline; the _rachis_ and the branches are stiff, slender and smooth, the lower branches are a little deflexed. [Illustration: Fig. 120.--Hygrorhiza aristata. 1. Branch; 2. part of a leaf with ligule; 3. spikelet; 4 and 5. glume and its palea; 6. lodicules and ovary.] The _spikelets_ are very narrow, sessile or pedicellate, articulated on the pedicel, 1-flowered and 1-glumed. The _glume_ is about 3/8 inch long (excluding the awn) and the awn is as long as the glume or slightly longer, lanceolate, with five strong nerves and the lateral ones forming thickened margins; the palea is as long as the glume. _Stamens_ are six and _lodicules_ two. Found in ponds and tanks. _Distribution._--All over India and Ceylon. 13. Trachys, _Pers._ These are softly, villous, diffuse annual grasses. The inflorescence consists of usually two (rarely three) divaricating spikes on a long peduncle. The rachis is herbaceous, broad flexuous, jointed and bearing at each joint a solitary globose cluster of two or three perfect 1-flowered glabrous spikelets surrounded by many short spinescent glumes of imperfect ones. The perfect spikelets are 4-glumed and the glumes are very unequal. The first glume is minute, tooth-like, nerveless. The second glume is long, linear-lanceolate, membranous, very acute, strongly 3- to 5-nerved. The third glume is the largest, obliquely ovate, or obovate-oblong, cuspidately acuminate, rigidly coriaceous, 9- to many-nerved, paleate or not, empty. The fourth glume is shorter and narrower than the lower one, linear-oblong, acuminate, chartaceous, smooth, dorsally convex, with incurved margins, bearing a bisexual flower, paleate, palea is hyaline as long as the glume, and the margins are inflexed below the middle. Lodicules are very minute or wanting. There are three stamens. The styles are very long with slender stigmas, exserted at the top of the glume. The grain is oblong, compressed, free within the glume and its palea. =Trachys mucronata, _Pers._= This is a diffusely branching, softly villous annual grass. The stems are many from the root, 16 to 18 inches long, ascending or decumbent and prostrate, leafy, glabrous, rooting freely at the lower nodes, especially when procumbent. The _leaf-sheaths_ are loose, inflated, hairy or rarely glabrous. The _ligule_ is a thin membrane, or a ridge of fine closely set hairs. _Nodes_ are villous.