RIVEE 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 

 Rhizophora mucronata (PI. LXIV) and Bruguiera gymnorhiza (PI. 

 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 moVucceTisis), known in the 

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

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

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

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



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

 are thickets of Nyjpa 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 

 algse, including species of Conferva and Enteromorpha, and Chara 

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

 {Thorea 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 tiliacewm. 

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

 open hillsides, the sword grass, XipJieagrostisfloridula. Where streams 

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

 with a tree fern {AlsopMla haenhei) and the widely spread Angiop- 

 teris evecta (PI. XXXIII). 



THE STRAND. 



The principal beach plant ia 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 ohtusifolium, with a similar habit of 

 growth, and frequently jfelastoma marianum, Vtgna lutea, a.ndJIelio- 

 tropium curassavicum. Among the beach shrubs are Lobelia koenigii, 

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

 fortia a/rgentea (PI. LXVIII), a boraginaceous plant with fleshy leaves, 

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

 dark anthers growing in scorpioid racemes; and Pemphis acidula, a 



