s 



Dansk Botanisk Arkiv, Bd. 2. Nr. 8. 



while at low water the trees stand with their trunks and bases 

 exposed to the sun, and the sea bottom is laid bare for wide 

 distances. In Rhizophora and Ceriops the arched aerial roots 

 from the branches make, together with the stems, the whole scrub 

 an inextricable confusion of grey stems, while as regards Avicennia 

 the sea bottom is covered by its numerous small vertical asparagus- 

 like aerial roots. The two photos (Plate I, Figs. 2 — 3) from Port 

 Hedland were taken from just the same spot, with an interwal 



Fig. 3. The steamer at low water leaning against the logs of the jetty at 



Derby. The sea has retired farther out than the steamer which stands on 



the naked sea-bottom (Nov. 7. 1914). Photo, by C. H. O. 



of 6 hours, and show low Avicennia at high water standing in 

 water until the crown, and at low water growing on the dry sea- 

 bottom. (In some depressions water was left by the retiring tide 

 and gives the impression that the bottom is not quite deprived 

 of water). 



The tides run with great force (10 — 12 knots at some places) 

 and only such well fastened plants as the mangrove trees are able to 

 stand it; therefore we do not find much vegetation between their 

 roots. Usually the soil is quite bare, hardly any sea-weeds and 

 no sea-grasses 1 being found. It was an exception to find the green 

 carpet of the Suæda mentioned above, and this was only near 

 the high water mark, where, probably, not every high water 



] Compare: The Sea-Grasses of W. A., in Contr. to W. A. Botany I, p. 7. 



