490 ECOLOGICAL STUDY OF SALTMARSH VEGETATION. 



the river, bordering Unwin's Bridge Road. In exceptionally 

 low tides the upper reaches of the channel are emptied and the 

 Ruppia lies exposed on the mud (Plate xxi., fig. 9). The banks 

 of the channel are lined on either side with a formation of 

 Triglochin striata Ruiz, et Paw, a stoloniferous perennial with 

 a wide extratropical range. The Triglochin is arranged in 

 narrow bands at the mouth of the channel where the tide flow 

 is strong and deep, broadening as the stream is ascended, the 

 bands on either bank finally becoming confluent in the shallow 

 headwaters. The zonal boundaries of the Ruppia and Triglochin 

 are regulated by the facilities for submergence, the formation of 

 the latter projecting at intervals into the stream, indicating, 

 beacon-like, the shoals of the channel. 



The Thatch-reed, Phragmites communis Trim, a cosmopolitan 

 cane-like grass with an elastic growth form, has established a 

 reed-bed in the saltmarsh on the banks of Cook's River at 

 Undercliffe . The section of the marsh selected by the Thatch- 

 reed receives a slight influx of drainage from the surrounding 

 hills, and in this station the formation — a pure culture — reaches 

 its optimum. In the tidal river it is restricted to a narrow 

 band along the bank, rarely descending into water more than 2—3 

 feet in depth. Of this species Warming (40, p. 189) writes: — 

 "It can grow in water 3 metres in depth." As shown above the 

 Thatch-reed does not invade tidal waters in the Port Jackson 

 district to the depth noted by Warming. 



In an article on the mitigation of floods by forestry opera- 

 tions J. H. Maiden (29, vi., 1917, p. 130) recommends 

 Phragmites communis as a useful grass for the protection of 

 river banks from erosion. A small patch of the Phragmites 

 detached from the reed-bed at Undercliffe, lying between the 

 banks of the river and the dry salt plain which is not affected 

 by the fresh water drainage, has developed a weak open growth 

 into which a formation of Triglochin striata has intruded, filling 

 the spaces between the thinly-ranked stems of the Thatch-reed 

 with a compact sward (Plate xxv., fig. 18).* Owing to the 

 greater depth of the rhizomes of the Thatch-reed their forma- 

 tions are noncompetitive, and, sheltered and stayed by the stout 

 culms of its tall associate, Triglochin striata — -more tolerant of 

 salinity than the Phragmites — here attains its full stature, 1—1 J 



* This photo was taken in August when the haulm-leaves 

 of the Phragmites were withered. 



