Observations on the microscopic alga which causes the discoloration of the sea in various parts of the world / by C. Collingwood.

  • Collingwood, Cuthbert, 1826-1908.
Date:
1868
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the microscopic alga which causes the discoloration of the sea in various parts of the world / by C. Collingwood. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    three passages. The fourth time was in winter (December), and during the height of the monsoon—the wind very bois- terous, and the sea very rough—so that the substance was doubtless so washed and thoroughly dispersed by the waves, as to be indistinguishable amidst the turmoil and foam. The most northerly point at which I observed its accumu- lations forming a pellicle upon the surface of the sea was at the north entrance of Formosa Channel, in lat. 25±° N., and the most southerly point was in Rhio Strait, on the equator. I have described the first specimens observed, from the Indian Ocean north of the line, as presenting under a lens the appearance of a sheaf (fig. a), hut this peculiar arrange- ment I did not elsewhere meet with. There were, in fact, two modes of aggregation of the vegetable filaments com- posing the Alga in question. Everywhere in the China Sea, in the South Indian Ocean, and in the Atlantic, the form presented was that of small cylindrical bundles, more or less pointed at one end, but obliquely truncated at the other (figs. b, c), having an average length of -^th to -roth inch. They were cream-coloured and opaque, and examination with a lens showed that the ends were fimbriated, owing to the component fibres being loose at their extremities. A third form was occasionally mingled with these, but in very small quantities. It was a minute spherical body, solid and opaque, about the size of an ordinary pin’s head, bristling with minute rays, like a miniature echinus (fig. g). This form I noticed in the North Indian Ocean, and very rarely in the China Sea, but, although associated with the sheaf- and wedge-shaped Alga, it appeared to constitute a very infinitesimal proportion of the scum upon those seas. I look upon it as a species of Oscillatoria. The appearances presented by all these three forms under the microscope are very similar, and the first two apparently identical. The body, whether sheaf- or wedge-shaped, is at first opaque, but gentle pressure shows each bundle to be composed of a dense mass of cylindrical filaments of unequal lengths, combined together and interlacing with each other, forming an intricate network, having the appearance of a complicated basket-work with the ends of the osiers sticking straight out, as when the work is unfinished (fig. d). Each filament is long, and beautifully symmetrical, unbranched, with a rounded extremity, and perfectly even, hair-like out- line. The filaments appear to be of equal diameter through- out their entire length, and are filled with a dark-green granular matter, which, before pressure is applied, renders