Mr. Thompson on an Alga which colours Bally drain Lake. 81 



whether like that plant it be originally fixed I am unable to 

 say. 



As my species does not correspond with any Anabaina of 

 Dory's, I venture to characterize it as follows : 



Anabaina ? spiralis, mihi. A. consisting of an extremely mi- 

 nute moniliform thread of a rich green colour, and regu- 

 larly spiral like a corkscrew; globules of equal size through- 

 out its entire length. 



The specimens obtained were invariably of similar breadth 

 and rarely presented more than four spiral turns, and when of 

 this size were y\j of an inch in length. The species at first, 

 when mingling with the water, is of a dark green colour : 

 when in calm weather it ascends to the surface in separate 

 particles, it appears pale green ; when it does so en masse (the 

 earliest symptom of decay), it is of a pale blue ; and in the last 

 stage of decomposition, ferruginous. Having on the 27th Sept. 

 brought home in several phials specimens of what I had pre- 

 sumed to be this plant in all its stages (i. e. from its first to 

 last appearance as a colouring matter), I was much pleased 

 to have the conjecture verified by microscopical examination. 

 A portion taken from the surface when it appeared pale 

 green, was under the microscope of as dark a hue as in July, 

 whilst the blue and ferruginous colours exhibited different 

 stages of decomposition. When in the most perfect state in 

 which the plant has occurred to me, the globules appear en- 

 tirely filled with granules, but when very highly magnified are 

 each found to be surrounded by a hyaline membrane. The 

 blue and ferruginous tufts exhibited generally the empty glo- 

 bules and the escaped granules scattered all about, but the 

 former were seen in every state from full to empty : some had 

 granules only in the centre, others were half-full, and some 

 separate globules were entirely filled with the granular mass. 



When two of the spiral portions come in contact, they have 

 an elastic power, by which they can, though slowly, disen- 

 tangle themselves and separate from each other, — a fact which 



globular and escape in moniliform threads." It grows "on stones, aquatic 

 plants, and the boards of sluices in early spring, forming a tuft of small ' 

 crisped somewhat intricate bundles of filaments, of a beautiful deep green." 

 — Berkeley's • Gleanings of British Algae.' 



