go The Irish Naturalist. September, 



Cooke after describing the plant, refers to Dr. Drummond's 

 account of his discovery of it in Ireland, which is so in- 

 teresting, and so exactly corresponds with my own obser- 

 vations that I think it is worth quoting in full. 



" 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 im- 

 memorial 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 to be perfectly transparent, and 

 it appears equalty clear at the edges of the lake, but at a 

 depth of two feet the bottom is indistinguishable and the 

 water presents a feculent opacity, accompanied 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 inumerable 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 discovered 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 about a foot and a half in length. These 

 seemed evidently 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 some- 

 times observed their motions to be very vivid, and in other 

 instances little or no motion could be perceived. 



" They are extremely minute, their traverse striae very 



