Other species of marine plants have their duty too. That which is known as the river mangrove (AEGICERAS MAJUS)--which does not confine itself to rivers--comes to sweeten the noisome exhalation of the mud, and with its profuse white, orange-scented flowers, to invite the cheerful presence of bees and butterflies. The looking-glass tree (HERITIERA LITTORALIS), with its large, oval, glossy, silver-backed leaves and boat-shaped fruit, stands with the river mangrove along the margin farthest from the sea, not as a rearguard, but to perform the function of making the locality the more acceptable to the presence of plants which luxuriate in sweetness and solid earth. Another denizen of the partially reclaimed area of the mangrove swamp is the "milky mangrove," or river poison tree, alias "blind-your-eyes" (EXCAECARIA AGALLOCHA). In India the sap of this tree is called tiger's milk. It issues from the slightest incision of the bark, and is so volatile that no one, however careful, can obtain even a small quantity without being affected by it. There is an acrid, burning sensation in the throat, inflamed eyes and headache, while a single drop falling into the eyes will, it is believed, cause loss of sight. Yet a good caoutchouc may be prepared from it, and it is applied with good effect to ulcerate sores, and by the blacks of Queensland and New South Wales for the relief of certain ulcerous and chronic diseases; while in Fiji the patient is fumigated with the smoke of the burning wood. Several of the plants produce more or less valuable woods. BRUGUIERA RHEEDI frequently grows slender shafts, favoured by blacks for harpoon handles on account of their weight and toughness. White mangrove provides a light, white tough wood eminently adapted for the knees of boats. The seeds resemble broad beans, and after long immersion in the sea will germinate lying naked and uncovered on the scorching sand, stretching out rootlets in every direction in search of suitable food, and expanding their leathery primary leaves--even growing to the extent of several inches--while yet owing no attachment to the soil. If it were not capable of surviving and flourishing under conditions fatal to most plants it could not contribute its quota to the formation of humus favourable to the progress of the advancing hosts of tropical vegetation.