Page:Transactions NZ Institute Volume 15.djvu/337

I have already mentioned that this plant, which was common here two years ago, has been very scarce of late: and no sign of conjugation has as yet come under my observation.

Holocystis incisa.

Mr. Archer unites this to Micrasterias (other authors, I find, include it under Tetrachastrum); and he states that instead of being identical, as I had thought, with Dr. Wallich's Indian plant, it is probably the same as a plant from Sweden, reported by Cleve and called M. decemdentata β upsaliensis.

Euastrum binale, Turpin.

The plant mentioned by me (vol. xiii., p. 306) as either this or E. elegans is certainly E. binale, as I have satisfied myself by comparison with Ralfs' figures, and with specimens in my English gatherings. E. elegans shows the sides of the terminal notch extending considerably beyond the lateral spines. I regret to say that the figure 26 in vol. xiii., pl. xii., is about as unlike the plant which it is supposed to represent as it is possible to be; and unluckily Mr. Archer has been misled by it to take my Euastrum for a new thing. My original drawing was meant to be, and I think was, almost exactly resembling Ralfs' figure 8 d (or 8 f) in his pl. xiv.

Cosmarium margaritiferum.

I believe that several of the forms supposed by me to belong to this species were really C. tetraophthalmum, C. broomeii, etc., or at least closely allied to them. C. biretum I have never seen here: C. botrytis is certainly common. The conjugation of C. margaritiferum I saw once, and could detect no difference from the European plant. In this case also the printed figures in pl. xii., vol. xiii., figs. 27, 28, and 29, are unsatisfactory. Fig. 28 was intended to show a slight truncation, but it does not show any.

Cosmarium crenatum, Ralfs.

If Ralfs' figure 7, pl. xv., be correct, our New Zealand form differs from the English one by having its ends (as my figure shows) straight, without crenations. I think also that the segments are somewhat wider at the base. Length of frond 30.5 μ; breadth 27 μ.

Cosmarium botrytis, Bory.

In examining this plant I have been able to detect a very decided voluntary motion, which on one occasion I observed for nearly three hours. As far as I can gather from works available to me, it has never been satisfactorily shown that the Desmidieæ travel voluntarily, that is, in the manner in which Diatoms travel. It has long been known that Desmids "move;" that is, they will come to the surface if buried in mud, or to the side of a vessel nearest to the light. But such movements as these, as Ralfs remarks (p. 22), may be due rather to the stimulus of light than to "voluntary