Dr. Dickie on the Colow of a Freshwater Loch. 21 



Professor Allman has more recently described (Annals of Na- 

 tural History, vol. xi.) a new plant, Trichormus incurvus, All., 

 as " colouring the water of the Grand Canal Docks near Dublin, 

 a pea-green." 



The present brief notice is for the purpose of recording the 

 occurrence of a species of Rivularia near Aberdeen, under cir- 

 cumstances similar to those of the plants alluded to and pro- 

 ducing a like effect. For some years back excursions have been 

 made with the students of my botanical class to a loch on the 

 estate of Parkhill, about four miles north-west from Aberdeen. 

 The sheet of water in question is about a quarter of a mile in its 

 greatest length; on almost all sides it is surrounded by extensive 

 deposits of peat, with the soluble matter of which a great pro- 

 portion of the water passing into the loch is impregnated. The 

 loch abounds in Scirpus lacustris, Arundo Phragmites, Nuphar 

 lutea, Nymphcea alba, and various species of Potamogeton, &c. 

 The locality was generally visited in the beginning of July; 

 nothing pecuhar had ever been observed till the summer of 1846, 

 when my attention was arrested by a peculiar appearance of the 

 water, especially near the edge, but extending also some distance 

 into the loch. Numerous minute bodies with a spherical outline, 

 and varying in size from a'^^h to y 2th of an inch in diameter, 

 were seen floating at different depths, and giving the water a pe- 

 culiar appearance. In some places they were very densely con- 

 gregated, especially in small creeks at the edge of the loch. A 

 quantity was collected by filtration through a piece of cloth, and 

 on examination by the microscope, there could be no doubt that 

 the production was of a vegetable nature and a species of Rivu- 

 laria ; one however unknown to me, and not agreeing with the 

 description of any species described in works to which I had 

 access. Specimens were sent to the Eev. M. J. Berkeley; he in- 

 formed me that the plant belonged to the genus mentioned, and 

 stated it to be Rivularia echinulata, E. B. Along with it, but in 

 very small quantity, I also found another plant, the Anabaina 

 Flos-aqua, Bory. 



In the first week of July 1 847, the same species were observed 

 similarly associated, but the Anabaina was now more plentiful, 

 without however any apparent corresponding diminution in the 

 quantity of the Rivularia. 



In July last (1848) it was observed that the Rivularia was as 

 rare as the Anabaina had been in 1846 ; to the latter consequently 

 the water of the loch now owed its colour, which was a very dull 

 green ; the colour however becomes brighter when the plant is 

 dried. In neither of the seasons mentioned was it in my power 

 to make any observations on the colour of the loch earlier or 

 later than the date above-mentioned, consequently nothing can 



