Art. VI.—Notes on a Plant (Glossostigma elatinoides) found beside the Maungapouri Stream, Otaki.
[Read before the Wellington Philosophical Society, 22nd August, 1888.] Glossostigma elatinoides, Bentham.
This plant is not uncommon in New Zealand, and I have lately found it beside a stream near Patea. It seems to grow so close to the water that at freshes it may be entirely submerged. It has been reported from Auckland, Nelson, and Southland.
The plant is a perennial creeper, flowering from November to March. It grows very close to the ground and very thickly.
Its botanical description is as follows:—
Root fibrous, springing from axils of leaves.
Stem prostrate, smooth, green, running; leaves and roots springing from nodes 1in. apart.
Leaves opposite, 2 at each node, succulent, simple, entire, obovate, pale-green, ⅓in. by ⅙in., petioled.
Flowers: Calyx regular, monosepalous, inferior; corolla irregular, monopetalous, campanulate, 3- and 2-toothed, creamy-white; stalk 1in.
Stamens definite, 4, epipetalous; anthers ovate, brown, erect, opening longitudinally.
Pistil leaf-like, spathulate, covered with minute spikes, at times curved over stamens. When touched gently, turns back and lies against the petals; being the same colour, it is then difficult to perceive. After being opened unnaturally, closes again in about a quarter of an hour.
Ovary superior, 1-celled (?).
Style long; stigma and style in one.
The peculiarity which distinguishes this curious little plant is that upon touching the pistil, which forms a kind of hood over the stamens, it rises up and falls back upon the petals, so closely fitting as not to be seen without trouble. This action leaves the stamens exposed to view.
Upon examination of many plants, I found that in about fifteen minutes after being disturbed the pistil resumes its former position.
The experiment can be repeated an indefinite number of times, I believe. The pistil will not remain over the stamens if pushed there.
It would seem as if there is a spring of some sort—if one can call it by that name—in the pistil, but as yet the microscope has not revealed it to me.
I am inclined to the view that this movement of the pistil is intended to produce cross-fertilisation, or to produce fertilisation at all. An insect alighting upon the pistil would probably cause it to turn back and so expose the pollen; this would be carried away and deposited on the next flower visited. The spikes with which the pistil is studded would facilitate this. I have, whilst examining the pistil, found grains of pollen adhering.
The pistil would close after the insect's visit, thus preserving the remaining pollen.
I noticed on the 30th January that all the flowers I got and examined had their pistils turned back, and so remained until the flower died.
After reading some papers by Mr. G. M. Thompson on cleistogamic plants, I have thought that this plant might be one in which self-fertilisation takes place, and until that had taken place the pistil remained over the stamens, and that when the organ had fulfilled its function it lay back for good. Upon further observation of a single flower, I noticed that, when water was poured round the plant so as to completely submerge it, the pistil, which was turned back upon the petals, closed over as the water reached it, and remained so, covering the stamens until the water was removed, when it again opened back.
A question still remains: Would pollen deposited upon the outside of the pistil fertilise the plant? If so, the insect carrying pollen would be obliged to leave some in opening the next flower visited.
The peculiar position of the pistil may be a wonderful contrivance for preserving the pollen from being washed away when the plant is submerged, as must often be the case.
The foregoing note has been drawn up as containing certain points of information, botanical description, &c., on this curious little plant which are not noticed in Mr. Cheeseman's paper, in vol. x. of the “Transactions,”* on the springing-back of the pistil. This feature is also of so exceptional a character that even repeated accounts of it are interesting.
[Footnote] * “Trans. N.Z. Inst.,” vol. x., art. xlvii., p. 353.