LYNGBY.E. 249 



In lakes and pools. 



This is the species which Dr. Drummond described as the " colouring 

 substance of Glasslough Lake, Ireland." He commences by skating that 

 " Glas-lough " signifies " green lake," an appellation given to it from 

 time immemorial on account of the hue of its waters, which exhibit a 

 green tinge, equal to, or exceeding in intensity, that of the sea, though 

 it is not at all times equally striking. " From the accounts I received, 

 the green colour is evident in the lough throughout the year, and if I 

 may judge from my own observations, every drop of it is impregnated 

 with the oscillatory filaments." " When a little of the water is lifted in 

 the hand it seems perfectly transparent, and it appears equally clear at 

 the edges of the lake, but at a depth of two feet the bottom is indis- 

 tinguishable, and the water presents a sort of feculent opacity, accom- 

 panied by a dull, dirty, greenish hue. On lifting some of this in a glass 

 it seems at first sight quite transparent, but on holding it up to the light 

 innumerable minute flocculi are seen floating through every part of it, 

 and producing a mottled cloudiness throughout the whole." "At first I 

 could only find the plant diffused through the water, but at length I dis- 

 covered a wet ditch extending from the lake into an adjoining field, and 

 there it appeared swimming on the surface in large masses several inches 

 in thickness, and above a foot and a half in length. These seemed evi- 

 dently to be produced by an agglomeration of the filaments floated in 

 from the lake, matted together at the surface, and increased in growth. 

 The surface of these masses, where dried by the contact of the air, was 

 of a bright bluish verdigris hue, while the parts immersed in the water 

 were of a dull opaque green. 



"On examining specimens in the microscope, I sometimes observed 

 their motions to be very vivid, and in other instances little or no motion 

 could be perceived. They are extremely minute, their transverse striae 

 very numerous, and at distances of about half a diameter from each 

 other. The filaments in the conglomerated masses appeared to me to be 

 many inches long, and running parallel together ; the broken fragments 

 dispersed through the lake cross each other in all directions." 



Plate XCVlll. fig. 5. Trichomes from specimen collected by Drurn- 

 moud X 400 diain. 



Oscillaxia tenuis. Ag. Syst. Alg. p. 60. 



Forming a bright green, or dark blue green stratum, shortly, 

 or elongated radiating. Trichomes straight, rather rigid, more 

 or less endowed with active motion ; joints equal or half as 

 long as broad, sometimes a little constricted at the dissepi- 

 ments, which are delicately granulated ; apex more or less 

 attenuated, obtuse, curved or straight ; cell-contents pale 

 watery blue. 



SIZE. Threads '054--006 mm. diam. 



Rabh. Alg. Eur. i., 102. 



Oscillatoria limosa, Hook Fl. Scot, ii., 79. 



Oscillaria viridis, Kutz. Tab. Phyc. i., t. 41, f. 6. Eng. Bot. 

 t. 2523. Johnst. Fl. Berw. ii., 264. 



Oscillatoria coritexta, Carrn. Hass. Alg. 256, t. 71 , f. 7, 4, 

 6. Eng. Fl. v., 376. Harv. Man. 165. 



Oscillatoria tenuis, Hass. Alg. 248, t. 72, f. 1. (?) Jenn. 

 Tunb. Wells 188. Harv. Man. 163. Grev. Fl. Edin. 303. 



