LYNGBY. 249 
In lakes and pools. 
This is the species which Dr. Drummond described as the ‘colouring 
substance of Glasslough Lake, Ireland.” He commences by stating 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 XCVIII. fig, 5. Trichomes from specimen collected by Drum- 
mond X 400 diam. 
Oscillaria 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 FI. Scot. ii., 79. 
Oscillaria viridis, Kutz. Tab. Phyc. i i, t.41,f,6. Eng. Bot. 
t. 2523. Jobnst. FL Berw. ii., 264. 
Oscillatoria contexta, Carm. 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. 
