BY A. A. HAMILTON. 47L 



The deepening of an arm of Cook's River, which traverses 

 the sewage farm near Arnclitt'e, has isolated a group of Man- 

 groves from their normal habitat, and left them stranded on a 

 pari of the marsh now drained by the channel. The Mangroves 

 have responded to the aeration of the soil, rendered possible 

 through the damming back of the tide, by dispensing with their 

 pneumatophores, a few only of the breathing roots remaining, 

 in a debilitated condition, at the base of their trunks. The 

 sweetening of the soil has encouraged the invasion of the Man- 

 groves by a grass and ruderal pasture (Plate xxvi., fig. 20) . 



The Mangrove is dependent on currents for distribution, a 

 mode of conveyance for which it is admirably equipped, the 

 fruit, with the seed in a more or less advanced stage of germina- 

 tion, falling within the range of tidal movement which promotes 

 its dispersal. When deposited on a mudbank the fleshy cotyle- 

 dons swell rapidly and rupture the leathery pericarp which is 

 then discarded, the roots simultaneously sprouting from the 

 quickly elongating hypocotyl and securing the young seedling 

 in position. The advanced stage of vivipary (40, p. 236) and 

 the extensive flotation of the seedlings (13, p. 76) attributed to 

 tropical members of the genus, do not occur in the local marshes . 

 In the Port Jackson district, Avicennia officinalis flowers in June 

 and its fallen fruits were seen in profusion on the mud-flats in 

 December . 



The Mangrove formation is surrounded, on the landward side 

 by a carpet of Salicornia which extends to the dry salt plain. 

 Of certain Molluscs found in the local marshes Hedley (18, p. 

 46 ) writes : — u These range from the fringe of glass wort, locally 

 (•idled 'samphire/ Salicornia australis, along the high-tide mark 

 downwards as far as the Avicennia grows." The association of 

 Mangrove and Salieornia is of frequent occurrence throughout 

 their geographical range, each occupying relatively similar posi- 

 tions on the marsh. 



The adaptable Salicornias are represented in all climatic zones, 

 but the Mangroves are largely restricted to tropical and sub- 

 tropical regions, only the hardier species venturing into colder 

 temperatures. Under normal conditions the boundaries of the 

 Salicornia meadow and the Avicennia arboretum are strictly 

 maintained, the dense thicket of pneumatophores presenting a 

 formidable barrier to intruders. On the banks of Duck River, 

 a few hundred yards below the dam separating the fresh and 



