1911-1912.] Elimination of A Igcs in Lochs and Ponds, 423 



Strangely enough, a few species of Diatoms have been 

 amongst the offenders, notably Asterionella, which is not 

 uncommon in our lochs, but in America is present in such 

 enormous quantities in some water-supplies as to be a veri- 

 table plague. But the plants which are most objectionable 

 belong to the group of the Blue-green Algae {Schizophycece), 

 certain of these possessing a natural odour and taste due 

 to the presence of an oil which, upon being liberated, is 

 said to be extremely disagreeable in its effects. In par- 

 ticular, two genera of the Blue-greens are very troublesome 

 as well as widespread in the States, namely, Anabcena and 

 Oscillatoria, Andbmna has the reputation of being " one of 

 the most prolific producers of a polluting oil that is known " ; 

 while Oscillatoria is not far behind in this respect, and is 

 said to be the cause of a most unpleasant odour and taste in 

 the water of reservoirs during the hot summer months. One 

 is somewhat surprised to learn that the motile Alga, Volvox 

 globator, so greatly prized by our microscopists when met 

 with, is also a pest, from its abundance in certain waters. 

 Uroglena has similarly caused considerable trouble. Like 

 Volvox, which it somewhat resembles, this motile form is 

 said to be " probably responsible for more trouble in water- 

 supplies than almost any other organism, either plant or 

 animal. . . . Each cell of the colony contains a nucleus, a red 

 spot, and a single greenish - coloured body, besides several 

 vacuoles. In addition, there is a considerable number of 

 oil globules, and it is the liberation of this oil which causes 

 the fishy, oily taste and odour produced by Uroglena. . . . 

 The exact nature of this oil is not very well understood. 

 It is believed, however, to be similar to the essential oils, 

 being non-volatile at the temperature of boiling water, and 

 seeming to resemble the oils obtained from Diatoms and the 

 Blue-green forms." ^ 



As showing how widespread and disastrous was the state 

 of matters in America, it may be mentioned that in 1902 

 a circular letter was sent to no fewer than 500 leading 

 engineers and superintendents of water - companies, asking 



1 'Year-book of the Department of Agriculture for 1892' (U. S.), pp. 182,183, 

 Art., "The Contamination of Public Water-Supplies by Algse," by George T. 

 Moore. (Also published separately.) 



