Page:Transactions NZ Institute Volume 15.djvu/341

Closterium selenæum, mihi.

Two of the distinguishing marks separating this plant from C. ehrenbergii are—the acuteness of the ends and the absence of a median inflation of the inner margin. The first character is constant and conspicuous. With regard to the second, I find that although, in its natural state, the inner margin forms a clear concave curve, yet in all the preserving fluids which I have tried an inflation becomes noticeable; not indeed such an inflation as that of C. ehrenbergii, but of the nature of that shown in my figure, where the inner margin becomes nearly straight. Indeed, in glycerine, it is sometimes quite straight.

I find also that when fronds are about to conjugate, an inflation is noticeable on both the outer and the inner margin, but only in the immediate region where the suture should be; that is, the cell-wall at that particular spot is bulged out all round. This, which is part of the process of conjugation, as I am about to describe, is quite different from the wide inflation visible in C. ehrenbergii.

The process of conjugation, however, as I have lately been fortunate enough to see up to a certain point, is the same as in C. ehrenbergii, as described by the Rev. W. Smith, in the Annals and Mag. of Nat. Hist., 1850, p. 1, and pl. i. Two fronds, each of which presents the slight bulging at the middle just mentioned, approach each other, and then become surrounded by a mucous envelope, within which they lie, longitudinally approximate, their ends almost touching, and their concave sides turned towards each other. Next, they proceed to undergo self-division: each frond separates at the middle, drawing itself out until, after the separation, there appear four fronds, each with one long arm and one very short arm, the latter terminating in a rounded short beak. Then the conjugation takes place by the junction of each corresponding pair, the junction being operated at the point where the bases of the long and short arms occur: and the endochrome, pouring out from each frond and joining in the middle, forms the zygospore, or, rather, the two zygospores, as there is one to each pair. Unfortunately, I cannot say precisely the nature of these zygospores. The specimens which I observed had been placed in a growingcell, where the process just described had been going on quite smoothly for more than twenty-four hours, from the first approach of the fronds down to the junction of the endochrome. At this point a sudden jar displaced the thin cover-glass of the cell: the conjugating fronds were crushed, and the process was at once brought to an untimely end. However, from what I saw, and from the presence in the gathering of bodies not otherwise identifiable, I have no doubt that the zygospores of C. selenæum are orbicular and smooth.