396 ZONES AND REGIONS [Pt. Ill, Sect. I 



Buch-Ham., S. acida, Linn., S. alba, Smith. Meliaceae : Carapa moluccensis, 

 Lamk., C. obovata, Bl. Myrsinaceae: Aegiceras majus, Gaertn. Rubiaccac 

 Scyphiphora hydrophyllacea, Gaertn. Verbenaceae -. Avicennia officinalis, 

 Linn., and var. alba, Bl. (sp.). AcantJiaccae : Acanthus ilicifolius, Linn. 

 Palmac : Nipa fruticans, Thunb. 



Many species of woody littoral plants occur at times on dry spots in 

 the mangrove, but very rarely on the mud (Heritiera littoralis in Ceylon, 

 according to Karsten). 



At high tide one looks from the sea on to bright green crowns of foliage 

 that rise out of the sea along the shore-line (Fig. 215), sometimes crowded 

 closely together, at other times like isolated outposts. At low tide, as far as 

 the mangrove extends, the ground is no longer covered by the sea, and 

 reveals itself as a bluish-black mud, from which the trees raise themselves 

 on short stems that are, however, supported by tall stilt-like roots (Fig. 216). 

 In the eastern mangrove, the species of tree which forms the advanced line 

 along the sea and which, by its slow forward march, causes a gradual 

 elevation of the coast, is Rhizophora mucronata (Figs. 215-217, and 

 227). No mangrove-tree is better equipped for resisting the movements of 

 the tide on the soft mud, for propagating itself under these difficult con- 

 ditions, and for recovering from the frequently quite undiluted salt 1 sea- 

 water the water lost in transpiration. The scaffolding of bow-shaped 

 stilt-roots supporting the stem represents a complete system of anchors, 

 which is strengthened by new roots growing down from the branches to 

 balance the growth of the crown. The leaves possess a marked xerophilous 

 structure (Fig. 17), with a thick cuticle, large mucilage-cells, protected 

 stomata, and especially a large-celled thin-walled aqueous tissue, the 

 dimensions of which increase with the age of the leaf and with the corre- 

 sponding rise in the amount of salt contained. Old leaves serve essentially 

 as water-reservoirs for the younger leaves. 



The mode of propagation is most remarkable in Rhizophora mucronata, 

 which in this respect agrees in the main with the other Rhizophoraceae 

 living in the mangroves (Fig. 218). The fruit, leathery and indehiscent and 

 about the size of a hazel-nut, soon after the completion of its growth is 

 pierced at its summit by the green hypocotyl, as the embryo does not 

 undergo any period of rest, but continues to develop without interruption. 

 The hypocotyl in Rhizophora mucronata is club-shaped and attains 

 a length of sixty centimeters, sometimes even more, before it falls down, 

 leaving behind it the fused cotyledons which served as absorbing-organs. 

 As its lower end is thicker, the seedling falls vertically, with its root-tip 

 downwards into the mud, and within a few hours develops roots that fix 



1 The statement frequently repeated in literature, that Rhizophora does not occur in 

 pure sea-water, is incorrect. I have seen R. mucronata thriving on the rocky ground of 

 the coral islands of the Java Sea, where there is no fresh water. 



