276 THE NATURALIST IN AUSTRALIA. 
Dr. Bancroft observed a white powder floating on the water and, on nearer 
investigation, discovered that it was being thrown off the surface of the vertical 
root shoots of the Mangrove. Examined more minutely, it was found that the cortex 
of these shoots were thickly riddled with pores which much resembled the so-called 
“Jenticels ” of ordinary plants. These pores communicated with an extensive system of 
air-passages which permeated the substance of the roots, and in the process of their 
enlargement threw off as broken down cellular tissue the powder observed floating 
on the surface of the water. These shoots, or aerial roots as they are more 
correctly termed, were thus demonstrated to be virtually a system of air-shafts 
which, projecting above the surface of the mud, secured for the roots abundant 
aeration and ventilation with every fall of the tide. It was owing to this efficient 
system of air-passages that the roots were preserved from becoming water-logged 
and rotten, as would happen to those of ordinary forest trees if submitted 
to similar conditions. A corresponding exaggerated lenticel-like aeration system 
was found by Dr. Bancroft to appertain to all of the peculiar root or trunk 
modifications possessed by the other species of Mangroves he examined. These 
included, in addition to the true aerial roots of Rhizophora next described, the nodular 
or knee-shaped woody protuberances developed from the ordinary horizontal roots in 
the genus Bruguiera and the greatly elongated vertical offshoots, much resembling 
those of Avicennia, possessed by Sonneratia acida, but which, in some instances, 
were elevated to a height of no less than six feet above the surface of the soil. 
The phenomenon of aerial, ventilating roots is most conspicuously manifested in 
the Red.or Orange Mangrove, Rhizophora mucronata, which occupies the greater portion 
of the photographic view reproduced in Plate XLIX. Arched, repeatedly bifurcating 
offshoots are in this type abundantly produced from the main trunk, while adventitious 
shoots that hang down and bifurcate in a similar manner are developed from the 
larger branches. Together they form a labyrinth of reticulations that in large 
plantations is often many acres or even miles in extent, and of such a height as to 
present an almost impenetrable barrier to the explorer. In most instances, moreover, 
the muddy ooze in which this species delights to grow, is of such depth and so soft 
and treacherous a character as to effectually debar all progress, except by recourse to 
the expedient of clambering upon the surface of the roots themselves. In locations, 
however, where the ground is firmer and the trees not so thickly planted, the 
naturalist may reap an abundant harvest and endless recreation within and without 
the precincts of a Mangrove thicket. On the outer, land-side, margin the specific 
