20 TRANSACTIONS OF THE [ Sess, LXxI. 
AERIAL Roors oF ACANTHORHIZA ACULEATA. By Miss 
BERTHA CHANDLER, M.A., B.Se. (Plates I. and IL.) 
The development of aerial roots is by no means an un- 
common occurrence among many plants. We find such 
plants as Rhizophora, Monstera, Ficus, Dillenia and others 
producing these organs under normal conditions: and, 
indeed, most plants may be induced to form these structures 
under conditions of excessive heat and moisture. 
Acanthorhiza aculeata, a palm, develops quite normally 
abundant aerial roots. They differ from normal aerial roots 
in the fact that at a certain stage of their development they 
lose their root-cap and become metamorphosed into hard 
woody structures, literally thorns. This curious fact about 
these roots was noticed as early as 1880 by Dr. Friedrich.* 
His examination was conducted almost entirely from the 
structural standpoint, for he deals with the development 
of tissues in these roots as they pass from normal aerial 
roots to thorns, and he touches very little on the physio- 
logy or function of these structures. 
There are two specimens of this plant in the palm-house 
in the Royal Botanic Garden, Edinburgh. A photo of one 
of these by Mr. R. Adam, is given (Plate I.). These speci- 
mens were studied with the permission of the Regius 
Keeper, and the results of my examination have made it 
possible for me to revise Dr. Friedrich’s paper, and to add a 
few further notes, together with figures which were not given 
by that author. He examined specimens in the Botanic 
Garden, St. Petersburg, and gives as an average length of 
a root about 10 cm. In the specimens in the Royal Botanic 
Garden, Edinburgh, some branched roots reach a length of 
40-50 cm., though the unbranched roots rarely attain a 
length of more than 15 cm. 
The external appearance of these aerial roots are readily 
seen from Plate I. They arise usually at the base of the 
leaves after the leaves have fallen away. The roots are to 
be seen in the figure developed roughly in rings round the 
trunk. Often they are developed, however, before this 
stage, and on tearing down the sheath covering the base of 
1“ Acta Horti Petropolitani,” 1880. 
