Plankton

Methods of Studying Plankton.

A veritable wonderland awaits the amateur naturalist who can spend a short time at the seaside during the spring months. He will require a student's microscope (magnifying 5o to 500 diameters) and some cheap, home-made apparatus. The net is simply a conical bag of the finest and strongest muslin obtainable: it is about 1 to 2ft. in diameter and about 4f t. long. Its mouth consists of an iron ring, to which a selvage of strong canvas is laced. The net is sewn on to this canvas edging. It is towed in the sea behind a rowing boat for about half an hour.

When the net is hauled it is drained of water and turned out side in. The pointed end is then rinsed in sea water contained in a 2 lb. glass jam jar. A small sieve is made by loosely tacking a piece of muslin on a square wooden frame about 4in. along each side. The water containing the catch is then slowly poured through the central part of the sieve. Then the latter is turned upside down and the plankton is washed off into a little sea water in the bottom of a saucer. This will now be a thick, greenish turbid

mass. A dipping tube is made (like a fountain pen filler, but with a wider opening) and some of the plankton is lifted with this and put into a watch glass, which is then examined under the microscope. Examined day by day the spring and summer plank ton is full of the most beautiful things.

Nets contrived to fish quantitatively are also used. In such investigations fine miller's silk bolting cloth is used. This has meshes of over 1 oo to the inch. Heaps of organisms escape through this net. To catch the very minute plankton the water must be centrifuged, or cultures are made in an analogous way to those employed by bacteriologists. Elaborate methods have been evolved for counting the organisms taken in a plankton catch.

BIBLIoGRAPHY.—There is a huge literature on plankton but many general papers are cited, and their source stated, in The Marine Plankton, by Johnstone, Scott and Chadwick (Liverpool, 1924).

A. J.)