Page:Transactions NZ Institute Volume 15.djvu/339

to raise itself on end, an operation which it took four minutes to complete. Having attained an upright position it remained there two minutes, waving gently to and fro, and then, all of a sudden, fell over on the other side. The "swarming" had now become quite violent, and the plant recommenced its travels, but this time in the contrary direction, returning towards the Pinnularia; after continuing thus for a minute or two it stopped, and then once more travelled away again. For half an hour it continued these manœuvres, sometimes going one way, sometimes another, always "elbowing" its way along, and in the main getting farther away from its original spot. Sometimes, when it stopped, it would roll about from side to side rather violently (but never from end to end). I thought I observed that as the "swarming" increased, so also did the "jerks," and it appeared to me also that the endochrome was changing. It showed a tendency to form in each segment two masses of closer consistency than the rest; each of these masses, retaining its bright green colour, became surrounded with a brownish band, and it was in this band (never in the green particles) that the swarming was conspicuous. Once an exceedingly minute Infusorium, scarcely visible under the ⅛ objective, came sailing towards the plant, somewhat leisurely; but, when almost on the point of touching it, darted suddenly back to some distance. Was it repelled? I could not say: it did not return.

The oscillations and rollings of the Cosmarium continued for two or three hours, and I observed that whenever it chanced to come to any little mass of weed or dirt obstructing its course it avoided it, sometimes indeed retracing its steps a little to get round a headland. Whenever it raised itself on end I took especial pains to see whether anything could be observed of the nature of cilia, or whether any appearance could be detected in the water leading to the supposition that retractile processes existed, but without success.

I have no doubt that the movements described were quite as "voluntary," as those of any Diatom. In another part of the same slide a Stauroneis was travelling very actively and the difference between the two plants was that the Diatom glided backwards and forwards without more than very slight oscillation, whereas the Cosmarium made its way simply by lateral jerkings.

Staurastrum gracile, Ralfs.

This is another of the plants in which the differences from the European form do not seem to me to be sufficient to render it distinct. As my figure shows, it is less slender and the processes are shorter than in Ralfs' species. Length in end view from the middle of one side to the end of the opposite process (exclusive of the four spines) 50 μ: length of process 15 μ.