480 ECOLOGICAL STUDY OF SALTMAESH VEGETATION. 



not ascend the dry marsh banks. Its numerous small seeds only 

 float for a few hours, the protective crustaceous seed-coat point- 

 ing to its dispersal by birds. 



The outermost series in the zonal succession on the flooded 

 marsh littoral is a J uncus association, which introduces a taller 

 type of vegetation with a cylindrical growth form. The stems 

 of these rushes are strongly built, the epidermis forming a 

 cylinder of bast, highly cutinised, and the walls of the air 

 cavities are arranged in a stout network binding the frame both 

 longitudinally and transversely. The lacunar tissue so well 

 developed in the Juncus is disadvantageous, as it increases trans 

 piration, but offers a modicum of compensation by storing a 

 supply of oxygen and lightening the stem structure. The firm 

 texture of the rushes enables them to advance into the weaker 

 formations of the succulents in their vicinity, wherever a change 

 in the edaphic conditions favours a forward movement. 



The dominant species in the local marshes is Juncus maritimus 

 Lam. var. australiensis Buchen., a tufted, shortly rhizomatic 

 herb. Its supremacy in this zone is rarely challenged, though 

 a Cyperaceous rush, Cladium junceum, R. Br., which extends 

 from Queensland south to New Zealand is an occasional com- 

 petitor in stations where the saline conditions operate in its 

 favour. At Buffalo Creek on the Lane Cove River, near the 

 bisection of the marsh by the Pittwater Road,, the (Indium and 

 Juncus run 'side by side along the marsh margin in parallel 

 bands ( Plate xvii., fig. 2 ) . At intervals the drainage, collected 

 into short gullies, enters the marsh, forming shallow bays on its 

 margin. The soil salinity in the bays is considerably reduced, 

 the dilution of the marsh water acting unfavourably upon the 

 Juncus formation. The more plastic Cladium, preferably a 

 lacustrine habitue, is not prejudicially affected by the influx of 

 fresh water and in these stations advances into the Juncus for- 

 mation, occasionally pressing through its ranks and occupying 

 a frontal position f Plate xviii., fig. 4) . An extensive formation 

 of Cladium junceum was noted on the margin of a lake in the 

 Centennial Park. In this habitat the conditions which confine 

 it to a narrow band on the marsh margin or the bank of a tidal 

 stream, i.e., the severe competition of the Juncus on its aquatic- 

 boundary, and the abrupt transition to a dry station on the land- 

 ward bank, are absent, and the Cladium spreads from the shallow 

 waters of the lake, in an irregular formation, into the adjoining 



