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Further Notes, read 16th October, 1895.
The following extract of a letter from Mr. A. Hamilton, informing me of the discovery of Dactylanthus at Tarawera, will be read with interest. It is dated 28th March, 1883 :—
“Some time ago, when I went to Lake Waikaremoana, you were kind enough to send me a list of plants which I should endeavour to find, and made particular mention of Dactylanthus taylori. Although at that time I was not fortunate enough to see or hear of any specimens, I have been on the look-out for it ever since, and last week, when collecting at Tarawera, on the Taupo-Napier Road, I found it.
“I was searching under the trees at the top of the ranges for Cordyceps robertsii, and picked up a scaly bud like an immature cone. On looking about to see where it had come from I found a tuberous-looking mass, about 10in. by 6in., covered with the circular scars from which these small spike-buds had fallen. Disposed irregularly round the mass were two different kinds of brown scaly spikes, the male (?) being much longer than the female. Remembering that you asked me to examine the manner in which it was attached to the root of the tree, I removed as much as possible of the vegetable mould and decaying leaves which partially covered the plant, and, finding a small tuber, bearing two or three good spikes, apparently distinct from the main mass, I carefully cut away the root of the tree and placed it, with the plant and the surrounding soil, in a box, carefully packing it with moss so that it could not shift. I then cut two or three of the mature male and female spikes from the larger plant, which I left carefully covered with branches. I tried to trace the root on which it seemed to grow back to the trunk of the tree, and uncovered it all the way. Even then it was hard to say what tree it was, as three—a Fagus, a Pittosporum, and some other —had their roots closely intermixed. Some little distance away I found the remains of another small mass, which had been broken up by a falling tree…. I carefully examined the tuberous portion, and found that, although it rested on the root of the tree, there was no attachment of any kind, but a woody root passed down the lower part of the tuber into the ground : this, unfortunately, I had cut through. The representation given by Taylor is fairly good, but the tuber seems to be growing from the root of the tree instead of on its own, and must have been from a larger specimen than mine.”
Mr. Hamilton has suggested a question of considerable importance, one perhaps that can only be determined by watching the development of the plant from the embryo. In the large specimen presented to the Colonial Museum by Mr. Hill the woody rhizome viewed from below presents every
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appearance of true root-parasitism, so far as can be determined without the destruction of the specimen; the same is to be seen in a specimen from Nuhaka which I exhibit to-night. At the same time, there can be no question that, as the woody rhizome extends over the surface of a large root, it adapts itself to the contour of the root without developing new organs of attachment—at least, in certain instances, probably in all.
On the other hand, I exhibit a young specimen the rhizome of which forms a small disc, scarcely exceeding lin. in diameter and ⅜in. in thickness; a tortuous woody root appears to have developed directly from the centre of the lower surface of the disc, and has attained a total length of 6in. or 7in. There is a very regular expansion of the supposed root upwards at the junction with the rhizome, and with our present knowledge it does not seem possible that this can have been produced by parasitism. For the present I hesitate to interfere with this root in any way until further specimens of a similar character can be obtained, when careful dissection of the point from which it is given off, and a microscopical examination of its structure, will doubtless throw light upon the subject. I have little doubt that specimens of this kind are more frequent than might be expected.
Mr. Hill assures me of his conviction that the plant is truly parasitic for the whole term of its existence, and that it never developes true roots. If we may suppose that it is at first parasitic and only produces true roots after attaining a certain stage of development, we have exactly the reverse of what takes place in such plants as Cuscuta, the radicle of which forms a true earth-root immediately after germination; but as soon as the stem produces haustella, which enable it to absorb the assimilated juice of some other plant, the root perishes. The process would be closely analogous to that exhibited by the native sandalwood (Fusanus cunninghamii), and the “eye-bright” (Euphrasia cuneata), &c., the roots of which become attached to those of other plants, and for a time at least absorb the chief portion of their nourishment in an elaborated condition. The facts, however, are still obscure, and much has to be done before the difficulties surrounding the subject can be properly cleared up. My only excuse for again drawing attention to Dactylanthus, while still unable to make any material addition to our knowledge of such an interesting organism, must be the hope I entertain that by this means the assistance of observers favourably situated for examining the plant in the living state may be more readily obtained.