238 HALOPHYTES 



a. The leaves are thick, coriaceous or somewhat fleshy, and entire : 

 Sonneratia, Lumnitzera, Carapa, Rhizophora, Avicennia. 



b. The epidermis is thick-walled and strongly cutinized ; the leaves 

 are often very glossy : Rhizophora Mangle. 



c. Various organs of the leaves of mangrove-plants have been inter- 

 preted by Areschoug * as hydathodes. In the mangrove on the coast of 

 Siam, Schmidt 2 found that glands on the upper face of the leaves of 

 Aegiceras corniculatum excrete salt. During the night the salt-crystals 

 absorb water from the atmosphere and deliquesce, but during the morning 

 the water again evaporates and the salt crystallizes out. In no other 

 species was the excretion of salt found by Schmidt. 



d. Stomata are often sunk beneath the general surface, and urn- 

 shaped anterior chambers are general. 



e. Aqueous tissue is always present, and sometimes massive. In 

 Rhizophora mucronata, the older leaves, which no longer assimilate, 

 become thicker than they were in youth ; this is caused by an enlargement 

 of the aqueous tissue : thus the leaf changes its function. 3 



/. The mesophyll is almost devoid of intercellular spaces, and the 

 palisade tissue is the sole or main chlorenchyma : Sonneratia, Lumnitzera, 

 and others. 



g. The nerve-ends dilate into water-storing tracheids i Bruguiera, 

 Avicennia, Ceriops, and others. 4 



h. Long stone-cells or bast-like mechanical cells are lodged between 

 the palisade cells in Rhizophora, Sonneratia, and Carapa, 5 and in the pith 

 of Rhizophora. 6 



i. Mucilage-cells occur in species of Sonneratia, Rhizophora, and 

 some others. 



j. Some species are strongly and densely clothed with hairs ; Avi- 

 cennia. 



k. The leaves assume a profile-lie 7 and consequently acquire isolateral 

 structure : Sonneratia, Lumnitzera, Ceriops, also Laguncularia. 



The cause of this xerophytic structure is to be sought in the physio- 

 logically dry soil, and in the position of the leaves, which are raised free 

 into the air and are exposed to intense tropical light, high temperature, 

 and wind. 



ASSOCIATIONS 



Various species may build up associations : 



Rhizophoretum occurs, for instance, and Acanthus unaided may form 

 mangrove-vegetation along estuaries. 8 



According to Schmidt nipetum belongs rather to fresh-water swamp. 9 



1 Areschoug, 1902. 2 Schmidt, 1903. * Haberlandt. 



4 See p. 126. 5 See p. 128. ' Warming, 1883. 



7 See J. Schmidt, 1903. 8 Tansley and Fritsch, 1905. 



' Cp. Tansley and Fritsch, loc. cit. From the extensive literature dealing 

 with mangrove, special reference may be made to Warming (1883), Johow 

 (1884), Gobel (1886), Schenck (1889), Schimper (1891), G. Karsten (1891), Haber- 

 landt (1893), Bprgesen and O. Paulsen (1900), Areschoug (1902), Schmidt (1903), 

 Tansley and Fritsch (1905), Holtermann (1907). 



