Art. XXXV.—Note on Splachnidium rugosum, Grev.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 25, 1892, Page 288

Art. XXXV.—Note on Splachnidium rugosum, Grev. By Robert M. Laing, B.Sc. [Read before the Philosophical Institute of Canterbury, 2nd November, 1892.] This interesting plant is a brown seaweed common on the coasts of both Islands, and growing a foot or two above lowwater mark. It seems to be an annual, as specimens of it are very scarce during the winter months. It occurs at the Cape of Good Hope, and on the Australian coast, as well as in New Zealand. It was first described by Linnæus as Ulva rugosa; but the genus Splachnidium was afterwards founded for its reception by Greville, and it still remains the only species of the genus. It has hitherto been included in the order Fucaceœ, because of its general external resemblance to them, and because it has conceptacles which were supposed to contain oogonia (v. “Phycologica Australica,” plate xiv., Harvey). However, in May, 1890, I was examining some specimens of this plant which were lying in a saucer exposed to direct sunlight, when I noticed a number of what I took to be oospheres entangled amongst the hairs of a conceptacle near the top of the stem. I mounted them on a slide with sea-water, and burst them by a slight pressure. A large number of zoospores filled with colouring-matter were at once extruded, showing that the bodies in question were sporangia, and that previous observers had been wrong in imagining them to be oospheres. The zoospores were actively swimming in the water, and cilia were distinctly visible on many. Most were egg-shaped, a few were approximately circular, and an eye-spot was frequently discernible. On another slide I obtained some which had come to rest and thrown off their cilia—whether after conjugation or not I cannot say. Since making these observations I have received a paper entitled, “On Splachnidium rugosum, the Type of a New Order of Algæ,”* Dulau and Co., Soho Square, London; 1892. by Margaret O. Mitchell and Frances G. Whitting, both of Newnham College. This contains an exhaustive description of the minute structure of the thallus and of the mode of growth; but the special feature of the paper is that the authors have arrived by indirect evidence at the conclusion that the bodies hitherto regarded as oogonia must be sporangia. Their examination of the plant shows that in its vegetative structure it is allied to some extent with the Fucaceœ (e.g., in the possession of a conceptacle), but that on the other hand

in its reproduction it is connected with the Laminariaceœ. The sum of its characters, however, is such as to expressly exclude it from any existing natural order. They therefore propose to establish the order Splachnidiaceœ for its reception. It must be very satisfactory to the authors of this excellent paper to find that the conclusion they have arrived at by theoretical considerations as to the reproduction of this plant is shown by observation to be justifiable and accurate. My own investigations, as far as they go, are quite in accord with theirs as to the minute structure of the thallus. Unfortunately, however, I have not been able as yet to examine the apical cell. It may be worth mentioning that I have invariably found a particular diatom in the mucilage of this plant. It is spindleshaped, and has a long elastic acicular process at each end. These processes are sometimes straight, sometimes curved or even hooked, and slightly clubbed. This diatom has been found in Splachnidium obtained near Wellington, and also in plants taken from Lyttelton Harbour. It may occasionally be found in the scrapings taken from the surface of the thallus. Those so obtained are more highly coloured with a characteristic brown pigment than those found in the interior, and appear (in some cases, at any rate) to escape through the ostiole. They may often be seen in slow motion, and are certainly worthy of further investigation.