71 
I carried them home for further examination. This powder, by the aid of a microscope, was found to 
consist of cells, iodine tinting them brown. This substance could have no relation to the reproductive 
system of the Avicennia tree as the flowers are high up on the branches, followed by fruits like garden 
ber.ns. 
The aerial roots of Avicennia are from a foot to 18 inches long, covered with green epidermis, on 
which the tides deposit mud and confervas. They never throw out leaves, but occasionally become forked. 
The muddy bank around the Avicennia stem is covered by a brush of these roots to a distance of from 4 
to 6 yards from the bole of the tree. 
This brush, by entangling debris, protects the bank from destruction by stream or tide. The roots 
are as thick as a pen-holder, and are covered with pores, 500 or more to be counted on a single specimen. 
The pores just opened are surrounded by broken epiderm, looking like the sepals of a flower, but having 
no regularity. The horizontal portions of the root system to which the aerial upright parts just described 
are attached are white, pithy, and full of air, and though living in undrained mud are quite free from any 
waterlogged condition. As the upright roots appear to rise out of the mud to obtain air, could the 
powder-discharging pores contribute anything towards aeration? Might they be mouths to admit air? 
After considering how this could be determined, I attached the indiarubber head of a pipette used for 
eye-drops to the cut part of a root, tied it, and immersed the aerial portion in water. On compressing the 
rubber cap, air was found to issue freely from the pores, and at no other parts. 
This, then, seems to me to be the function of the pores, to supply air to the root system of the 
mud-inhabiting Avicennia tree; the office of the discharged powder being to establish a communication 
between the air vessels of the plant and the outer atmosphere, by bursting open the cuticle of the root. 
The lenticels of the generality of trees differ somewhat from the root-pore in having no cup-like 
margins, and the corky mass does not fall freely in the form of powder, as is found in the roofc of 
Avicennia. Yet air can be blown through these organs among the foliage of Aegiceras, less freely in 
Excaecaria. With Paquelin's bellows and patience, it may be seen to issue from the lenticels on the young 
shoots of the peach, and by the same apparatus can be made to pass through the stomata near the midrib 
of the common Oleander. So far, I have seen air issue through the stomata of no other leaf, though 
experimenting with many. 
Excaecaria agallocha has a largo well-formed aperture, in which a brown powder is to be seen. I can 
blow air by the mouth applied to the cut stem, through all these apertures, but find the bellows of 
Paquelin's thermo-cautery a very convenient instrument for such experiments. (Bancroft, p. 328). 
The roots that show the greatest resistance to the passage of air, are those of the Excaecaria. The 
habitat of this tree is not in such close proximity to the shore as that of Avicennia, Rhizophora, or 
Aegiceras. 
The same organ I saw on dried stems of Acanthus ilicifolia, another shore plant. 
Guided by the appearances on the roots of Aegiceras and Excaecaria, the pores of which are found 
to extend also higher up among the foliage, the conclusion is forced on me that these root-pores are only 
modifications of the organs called lenticels (p. 329). 
The last is the " Blind-your-Eyes " of Australia because of its acrid juice. Blatter, 
at p. 653 of a paper to be presently cited, refers to some of its morphological characters, 
but does not refer to its pneumatophores. 
At p. 330, with Plates xx, xxii and xxvi, Bancroft refers to the " breathers " 
(pneumatophores) of Sonnemtia acida Willd. (Lythrariaceso). They are up to 6 feet 
high- 
Similar remarks as to breathing roots and stilt-roots may be made in regard to 
another Mangrove (Bruguiera Rheedii), from Queensland, in Dr. Bancroft's paper, 
p. 331, with good illustrations at Plates xix and xxi. The whole of Dr. Bancroft's 
paper will well repay perusal. 
