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112
HYDROCHARIDEA

Various methods of treatment have been employed, but the results are unsatisfactory. Compression of the head by bandages, and the administration of mercury with the view of promoting absorption of the fluid, are now little resorted to. Tapping the fluid from time to time through one of the spaces between the bones, drawing off a little, and thereafter applying gentle pressure, has been tried, but rarely with benefit. Attempts have also been made to establish a permanent drainage between the interior of the lateral ventricle and the sub-dural space, and between the lumbar region of the spine and the abdomen, but withouth satisfactory results. On the whole, the plan of treatmen which aims at maintaining the patient's nutrition by appropriate food and tonics is the most rational and successful. (E. O.*)


HYDROCHARIDEAE, in botany, a natural order of Monocotyledons, belonging to the series Helobieae. . They are water plants, represented in Britain by frog-bit (Hydrocharis M onusranae) and water-soldier (Stratiotes aloides). The order contains about Bfty species in fifteen genera, twelve of which occur in fresh water while three are marine: and includes both Boating and submerged forms. Hydrocharis Boats on the surface of still water, andehasrosettes of kidney-shaped leaves, from among which spring the Bower-stalks; stolons bearing new B leaf rosettes are sent out on all sides, the plant thus propagating itself iin the same way as the strawberry. Stratiotes aloides has a rosette of stiB sword- surface; it is- also like leaves, which when the P13111 is in1Bower project A above the

FIG. 1.-Hydracharis Mar.vus-ranae-Frog-bit-male plant. I, Female Bower. 2, Stamens, enla ed. Barren istil di? male Bower, enlarged. stoloniferous, the young rosettes sinking to the bottom at the beginning of winter and rising again to the surface in the spring. Vallisneria. (eel-grass) contains two species, one native of tropical Asia, the other, inhabiting the vwarmer parts, of both hemispheres and reaching as far north as south Europe. It grows in the mud at the bottom of fresh water, and the short stem bears a Elodea canadensis or g-amous Bowers 2, Prstil mp female flower. ¢1Sr¢r °f 10118, narrow 5, Fruit. i grass-like leaves; new 6, cut transversely. plants are formed at g, 9, Floral diagrams of male and female the end cf honmntal Bowers respectively. runners. Another type s, Rudimentary stamens. is represented by water-thyme, which has been introduced into the British Isles from North America. It is a small, submerged plant with long, slender branching stems bearing whorls of narrow toothed leaves; the Bowers appear at the surface when mature., H alophila, Enhalus and Thalassia are submerged maritime plants found on tropical coasts, mainly in the Indian and Pacific oceans; Halophila has an elongated stem rooting at the nodes; Enhalus a short, thick rhizome, clothed with black threads resembling' horsehair, the persistent hard-bast' strands of the leaves; Thalassia has 3 creeping rooting stem with upright branches bearing crowded strap-shaped leaves in two rows. The Bowers spring from, or are enclosed in, a spathe, and are uni sexual and regular, with generally a calyx and corolla, each of three members; the stamens are in whorls of three, the inner whorls are often barren; the two to Bfteen carpels 'form an inferior ovary containing generally numerous ovules on often large, produced, parietal placentas. The fruit is leathery or Beshy, opening irregularly. The seeds contain a large embryo and no endosperm. In Hydrocharis (fig. 1), which is dioecious, the Bowers are'borne above the surface of the water, have con- spicuous white petals, , contain honey and are pollinated by in- sects. Straiiotes has similar Bowers which come above; the 'surface only for P0llinatio1 becoming sub- merged again during ripening of the fruit. In Val- lisneria (Bg. 2), A which-is also dioecious, the small male Bowers are borne in large numbers in short~ stalked spathes; the petals are minute and scaleiéi


like, and only two of the three stamens are fertile; the Bowers y become detached Male plant', before opening and rise to the surface, where the sepals expand and form a Boat bearing the two projecting semi-erect stamens. The female Bowers are solitary and are raised to the surface on a long, spiral stalk; the ovary bears three broad styles, om which-some of the FIG.,2.-Vallisnerfia spiralis-Eel grass about % natural size. A, Female plant; B, laige, stiézhy p ' Q vpo en-grains rom

Bowers get 'de- pofifed (is 3)- After pollination the female Bower becomes drawn " below the surface t°- -5 by the spiral con- traction of' the long stalk, and the fruit ripens ' near the bottom. Eladea has poly- FIG 3, (that is, male, .female and hermaphrodite), solitary, in slender, tubular spathes; the male Bowers become detached and rise to the surface; the females are raised to the surface when mature, and receive the Boating pollen from the male. The Bowers of H alophila are submerged and apetalous. The, order is a widely distributed one; the marine formS are tropical orrsubtropical, but the fresh-water genera occur also

the temperate zones., ,