PRESIDENTIAL ADDRESS. 75 



the rocks may be, sometimes, blackened by a thick crust 

 of the small mussel, Modiola pulex. 



In concluding this account of the Ecology of Sydney 

 beaches, let me express a hope, that brief, disconnected, 

 and superficial though it be, yet may it serve as an invita- 

 tion to the pursuit of this fascinating study. 



EXPLANATION OF PLATES. 



Plate I, Fig. 1. 



A Mangrove forest in Upper Lane Cove, seen from without at 

 high spring tide. The lower branches of the Avicennia are here 

 dipped deep in the water. 



Plate I, Fig. 2. 



Another mangrove forest, at Sugar-loaf Creek, Middle Harbour r 

 seen from withimat low spring tide. Here the water has retreated 

 out of sight. A gleam of sunshine penetrates the dense shade and 

 illuminates a thick crop of pneumatophores in the foreground. 

 The Avicennia trunk in the middle of the picture is about two 

 feet in diameter. 



Plate II, Fig. 3. 



General view of the zosteretum at Roseville Reserve near the 

 head of Middle Harbour, seen at low spring tide, In the fore- 

 ground, the leaves of Zostera nana are awash, beyond, they are 

 exposed dry over an area of several acres. Towards the house- 

 boat in the distance is an expanse of bare mud, on which some 

 Avicennia seedlings have grown knee high. Here is a Pyrazus- 

 Holoecius zone. On the opposite shore along the water's edge are 

 more mangroves. 



Plate II, Fig. 4. 



A field of Hormosira banksii, Decaisne, seen at low spring tide 

 from Long Reef, looking north towards Collaroy Beach. In the 

 foreground the individual plants of the hormosiretum may be 

 easily distinguished. 



