115 



A NOTE ON TWO INSTANCES OF "BREAKING 



OF THE MERES." 



By James Burton. 



{Read April 2Qth, 1910.) 



The follo^ving paragraph occurs in tlie report given in The 

 English Mechanic oi the Club's excursion to Totteridge, July 10th, 

 1909 : " A small pond at the roadside was noticed, the water of 

 which was turbid and yellow, as though from clay in suspension. 

 On a hasty examination, however, the presence of some organism 

 was suspected. Under the microscope this was made out to be 

 one of the Myxophyceae probably Oscillatoria decolorata West 

 perhaps the same as 0. ochracea Grev. These lower algae are 

 not easy to discriminate ; should, however, this example prove 

 to be as expected, its presence in sufficient number deeply to 

 colour the entire pond would be an interesting instance on a 

 small scale of a phenomenon known as ' the breaking of the 

 meres,' when large bodies of fresh water lakes, etc., become 

 temporarily discoloured and rendered unfit for use owing to 

 the excessive multiplication of some of the same class of algae." 



I want to bring before you a few further details of this 

 occurrence, and also of a similar case I noticed soon after. 

 Probably not many members have paid attention to the pheno- 

 menon known as " the breaking of the meres," notwithstanding 

 the interest attaching to it. It may be defined as that con- 

 dition of a body of fresh water when it is so permeated with 

 one or more species of microscopic algae as to be visibly affected 

 by their presence. Of course, this definition would include those 

 very common instances where small ponds and roadside pools 

 are coloured by the enormous multiplication of Evglena or 



