ALG^. 135 



shorter, and often broken. Sometimes the oscillating 

 motion was very vivid, but at other times it could 

 scarcely be observed. No investigation could throw 

 any light upon the prevalence of this particular alga 

 in this one lake. There was nothing in its surround- 

 ings or the vegetation of the banks which would 

 aiTord any clue to the mystery, and the story of the 

 "green lake " remains a romance of low life. 



Subsequently Dr. Dickie announced the appearance 

 of the same alga, under similar circumstances near 

 Aberdeen. He says, " I have found the same species 

 particularly abundant in a small and shallow artificial 

 lake, in sheets of great extent at the bottom. I have 

 not observed it ' broken into innumerable fragments, 

 and suspended like cloudy flocculi in the water.' It 

 sometimes, however, becomes detached from the 

 bottom, and forms large masses on the surface." ^ It 

 is not by any means an unusual condition for the 

 filaments of an Oscillaria to become separated and 

 diffused through the water. We may not know the 

 precise condition under which this dispersion takes 

 place, but it is a matter of experience, not only that 

 Oscillaria will adhere together in large matted sheets 

 of considerable extent, but that it will also under other 

 conditions be severed and suspended. There is still 

 so much which we do not know in relation to the 

 OscillaricB, that what we really do know seems to be 

 only a small proportion of what is unknown. Why 

 and how do the filaments oscillate ? How is each 

 species propagated and continued .-* Are there any 

 reproductive organs, and of what character .'' Or is 

 ' Annals of Natural History, January, 1S49, p. 20. 



