![Thumbnail: [Volume 41, 1908 page 405]](/journals/rsnz/images/rsnz_41/thumbnails/rsnz_41_00_0427_0405_ac_02.gif)
Art. XXXIX.—Note, on Aerial Rhizomes in Cordyline australis.
[Read before the Philosophical Institute of Canterbury, 4th November, 1908.]
As is well known, the common New Zealand cabbage-tree (Cordyline australis) sends deep down into the ground a continuation of its ordinary upright-growing trunk, from which it differs in its positive geotropism, possession of roots, and rudimentary scale-like leaves. This rhizome functions not merely as an anchor for the plant, which is kept in place by the spreading horizontal or semi-horizontal roots; but it serves as a storage-organ for food, on the relative amount of which depends, doubtless, the blooming of the tree. If the trunk be cut off below the level of the ground, new aerial negatively geotropic shoots will be produced, and, vice versa, if the cut-off aerial portion can be induced to grow, a new positively geotropic shoot (rhizome) will be produced at its base. Frequently the trunk will put forth from any part ordinary leafy shoots, and occasionally near its base small positively geotropic rhizomes will be developed.
Some years ago the Hon. E. C. J. Stevens, M.L.C., called my attention to a fine specimen of Cordyline australis growing in the grounds of the Christchurch Club, which had a profusion of aerial rhizomes issuing from its trunk, not from near the base, but at a considerable distance from the ground.
![Thumbnail: [Volume 41, 1908 page 406]](/journals/rsnz/images/rsnz_41/thumbnails/rsnz_41_00_0428_0406_ac_02.gif)
The trunk of this tree is at the present time about 34 cm. in diameter, the actual base being swollen and wider. At 1.8 m. from the ground it gives off four erect branches, and it is at this point that the bunches of rhizomes are situated, though not merely at the forking, but to within 1.25 m. from the base of the tree. Plate XXIX gives a far better idea of the appearance, &c., than any detailed description. The largest bunch of rhizomes is 38 cm. long and 18 cm. deep. These bunches arise from lateral branches being freely produced, and which, through their positive geotropism, are brought close together. A rather large branch measures 18 cm. in length and 17 mm. in diameter. Short rudimentary lateral roots pass off horizontally from their sides.
Regarding the cause of this abundant growth of aerial rhizomes I can say nothing. The tree is at present rapidly dying, and the growth may be in the first instance pathological. It is not altogether dependent on the branching of the tree, since some of the rhizomes are given off far below the forking; others, again, where there is no branching, on one of the primary branches. It is evident, however, that under certain conditions—at present unknown—Cordyline australis can put forth from presumably the same tissue either an ordinary leafy ascending shoot or a rhizomatous descending one.