47 ECOLOGICAL STUDY OF SALTMARSH VEGETATIOX. 



dispensable office. Numerous references to the flotation and 

 germination of the seeds of plants represented in the local 

 marshes will be found in (13), (14), (15), while viability tests 

 of seeds of plants herein noted are tabulated by Ewart (11) and 

 Rees (35) . 



T h e F o r m at % o n s. 



1. The Tide-flooded Zone. 



The vegetation of the tidal zone is furnished chiefly by the 

 Grey Mangrove and the SaUcomia, supported by a series of low 

 succulents and salt-grasses, with a background of closely-regi- 

 mented reeds. In the marsh, this zone is bounded by the barren 

 salt plain, but on the landward margin the tidal formations fol- 

 low the bank inland until they reach the fluvial zone. The 

 Grey Mangrove, an umbrageous tree which forms dense forests 

 on its seaboard, is the pioneer colonist of the saltmarsh. lu 

 many of the local estuarine marshes the mangroves spread out- 

 wards across the tideway, following inland, in belted formation, 

 the banks of the customary drainage channel flowing through the 

 centre of the marsh. The extension of the Mangrove forest is 

 strictly limited by the depth of the tidal waters, its entry into 

 the bay usually taking the shape of a crescent encircling the 

 area at the head of the muddy basin lying behind the per- 

 manently flooded expanse of the bay, which is exposed at low 

 tide. Inland, the trees which have followed the course of the 

 channel to its broken headwaters, display, in a marked manner, 

 loss of size and vigour as they approach the shoals. Typical 

 examples of this graduated dwarfing occur in the marshes at 

 Homebush Bay (Plate xxii., fig. 12) and Cronulla, the reduc- 

 tion in stature commencing where the dilution of the tidal water 

 by the fresh water from the inland drainage channels becomes 

 effective . 



The root system of the adult Mangroves is shallow, radiating 

 horizontally and beset with the characteristic asparagoid 

 pneumatophores, which indicate the course traversed by the 

 roots from which they arise. In addition to fulfilling their well 

 known function of aeration, the breathing roots afford a power- 

 ful stay to the Mangroves, their partially embedded stems offer- 

 ing a stout resistance to the wash of the tide. Incidentally they 

 collect a considerable quantity of detritus and play a prominent 

 part in the uplift of the marsh. 



