Coloured Organisms on Sea-Sand

Abstract

A VARIED and interesting field of investigation awaits the microscopist who will make a detailed examination of the minute fauna, and flora of apparently barren sands on the seashore. To-day, on landing at the island of Oronsay at low tide, the otherwise pure white sand was seen to be coloured pink in one area, for an extent of several yards, green a little further up the beach, and golden-brown in small patches here and there. On examining samples with the microscope the brown colour was found to be due to living diatoms (not dinoflagellates in this case), naviculoid forms like Caloneis; the pink is formed of amorphous masses of fine granules in a jelly loosely adhering to the sand-grains, and may perhaps prove to be bacteria in a zoogloea state, while the green is caused by patches of a very simple alga (? a Coccophycid) made up of groups of rounded green ceils in a single layer on the sand-grains. I have kept samples of all the organisms and will submit them to a botanist for more precise identification. No Amphidinium patches were present so far as I could see. The variety of organisms present in the one little bay, the extraordinary abundance in each patch, and the brightness of the colour produced on the white sand were very striking, and seemed worthy of note.