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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    I will first state the localities in which I have observed this substance, and its general aspect, and afterwards describe the microscopic appearances presented by it in various places. I saw no large patches or discoloration of the sea through it anywhere in the Indian Ocean, either north or south of the line, in a single passage across each, hut, as I have just stated, the first traces of it appeared to me in the North Indian Ocean in March, So in the South Indian Ocean in May, lat. 28° 29' S., and long. 38° E., I again observed the sparkling appearance in the water, and once more found it to be due to “ dust,” but not of the sheaf form, but in wedge- shaped bundles to be presently described. In the Atlantic, I only once observed it, viz,, in June (lat. 8° 28' 5 S., and long. 28° 82' W.), when, standing on the fore- castle one day, my attention was arrested by the sparkling in the water which indicated the presence of sea-dust, and pre- sently after we crossed three long narrow streaks of the Alga thickly accumulated upon the surface. This was the only accumulation I ever observed out of the China Seas, and we are thus reminded of the “ bandes vertes ” observed by Chamisso between Teneriff and Brazil, in 1811. But the China Sea appears to be the home of this minute vegetable. Having left Singapore behind, the appearance of sea-dust became an every-day occurrence, in all its remark- able and interesting features. Nearly every day while tra- versing this sea more or less of it was to be seen, sometimes a mere sparkling appearance, while sometimes, and not un- frequently, the sea was covered with a thick scum of a yellowish-brown colour, like that which settles upon a stag- nant pond. The sea in some places was entirely hidden by the accumulation of the Alga, which, in calm weather, pre- sented the appearance of a regular, smooth, cream-coloured pellicle, thrown up here and there into thick folds and rugosi- ties ; and where thickest of a dirty yellow colour, but never red. Such a scum would cover the sea for nearly the whole day, with little interruption. But if a moderate breeze were blowing, and the sea were raised, instead of an uniform pellicle, the dust would be arranged in long irregular parallel lines, bands, or streaks, extending unbroken as far as the eye could reach, and always taking the direction of the wind. On one occasion we crossed a single band of this character, the only one seen during the day. When the sea becomes rather rough, the substance is more dispersed, and I have traced the bands under such circumstances with some diffi- culty. Out of four times that I crossed the China Sea, I observed these appearances, more or less well marked, during