260 THE AMERICAN MONTHLY [Sept. 



which some of the essential oils can be recognized by 

 tasts. 



Oil of peppermint 1 : 50,000,000 



Oil of cloves 1 : 8,000,000 



Oil of checkerberry 1 : 7,000,000 



Oil of cassia 1 : 6,250,000 



Oil of bergamot 1 : 6,250,000 



Cod-liver oil 1 : 1,000,000 



Kerosene oil 1 : 800,000 



Synura is generally found in surface waters where 

 there is a considerable quantity of organic matter. It 

 does not thrive at high temperatures, and is almost al- 

 ways absent from the water during the summer months, 

 or when the temperature of the water is above 55° F. 

 Only once in the last four years has a growth of Synura 

 been found in Boston water between May and October. 

 The exception was in September, 1891, in Lake Cochit- 

 uate, where there was a considerable growth at the mid- 

 depth ; but even there the temperature was below 55° F. 

 There are, however, rare instances in which Synura has 

 been found in hot weather, as for instance in Walden 

 pond, Lynn, Mass., in August, 1891. 



In September, 1891, Synura was present at the mid- 

 depth of Lake Cochituate, where it imparted a slight 

 taste to the water. Its distribution at this time was 

 something peculiar. The growth was confined to the 

 vicinity of the deep hole near the gate house, and, more- 

 over, was found only in a stratum about 10 feet thick, 

 about 55 feet below the surface. The temperature of 

 this stratum was between 48° and 50° F, The layer of 

 water immediately below the Synura had a decided 

 cloudiness and contained considerable Crenothrix. These 

 conditions prevailed for about a montb, during which 

 the Synura varied from 20 to 70 standard units per c.c. 

 (One standard unit equals 400 square microns.) The 



