Dr. Dickie on the Colour 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, Nymphea alba, and various species of Potamogeton, &c. 
The locality was generally visited in the beginning of July; 
nothing peculiar 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 jth to th 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 Rev. M.J. Berkeley; he in- 
formed me that the plant belonged to the genus mentioned, and 
stated it to be Rivularia echinulata, EK. B. Along with it, but in 
very small quantity, I also found another plant, the dnabaina 
Flos-aque, Bory. 
In the first week of July 1847, 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 
