RIVER AND STRAND VEGETATION. 53 



which form dense thickets and extend far out into the water at high 

 tide. Among those which send down aerial roots into the mud are 

 JRhizophora mucronata (PL LXIV) and Hruguiera gymnorhiza (PL 

 XL), both of which have large, opposite, entire, smooth leaves, and 

 fruit which germinates before dropping from the tree. They are easily 

 distinguished, the former having a four-parted perianth and the latter 

 having 10 to 14 calyx segments and petals. Associated with these are 

 found red-flowered Lumnitzeras, small trees belonging to the Combre- 

 taceae; Xylocarpus granatum (Carapa moluccensis), known in the 

 East Indies as the "cannon-ball tree," on account of its hard, spherical 

 fruits; and on adjacent firmer ground, Excoecaria agallocha, some- 

 times called the ''milky mangrove" or the "blinding tree," the acrid 

 juice of which is called "tigers milk" in the East Indies. 



RIVERS. 



Near the mouths of most of the rivers, where the water is brackish, 

 are thickets of Nypa fruticans, a stemless palm with great pinnate 

 leaves, which furnish the natives with excellent material for thatching 

 their houses. Associated with it are large simply pinnate ferns, 

 Acrostichum aureum (PI. IV), of wide distribution throughout the 

 warmer regions of the globe, and growing submerged are species of 

 Potamogeton and Ruppia maritima. There are also green, filamentous 

 algae, including species of Conferva and Enteromorpha, and Ckara 

 Jibrosa. Near the sources of some of the streams a small red alga 

 (Tkorea gaudichaudii) is found growing to rocks. On the banks of the 

 rivers near the sea beds of Pancratium littorale occur, together with a 

 creeping aroid, Cocos nucifera, screw pines, and Pariti tiliaceum. 

 Higher up the stream there are beds of reeds (Trichoon) and, on the 

 open hillsides, the sword grass, Xipheagrostisfloridula. Where streams 

 flow through shady forests several cordate-leaved aroids occur, together 

 with a tree fern (Alsophila Jiaenkei) and the widely spread Angiop- 

 teris evecta (PI. XXXIII). 



THE STRAND. 



The principal beach plant is Ipomoea pes-caprae, often called ' ' goats- 

 foot convolvulus," from the shape of its leaves. Its long, prostrate 

 stems form a carpet over the sand without twining or taking root, 

 and bear large, rose-purple, funnel-shaped flowers. Associated with 

 it is the leguminous Canavali obtusifolium^ with a similar habit of 

 growth, and frequently Melastoma marianum, Vigna lutea, and Ilelio- 

 tropium curassavicum. Among the beach shrubs are Lobelia Jcoenigii, 

 with thick, glabrous leaves, and white, zygomorphous flowers; Tourne- 

 fortia argentea (PL LXVI1I), a boraginaceous plant with fleshy leaves, 

 covered with silky white hairs, and white, heliotrope-like flowers with 

 dark anthers growing in scorpioid racemes; and Pern/phis acidula, a 



