100 Rhodora [JUNE 
odors, which have been likened to that of grass, fish, ripe cucumbers, 
candied violets, etc. Sometimes the odor is accompanied by a fishy, 
oily taste, and there are algae which impart a characteristic taste with- 
out any odor. Anabaena is one of the most troublesome genera pro- 
ducing these natural odors. It gives rise to a strong scent not unlike 
the odor of raw green corn, or nasturtium stems. Coelosphaerium, 
which frequently occurs with Anabaena, is also the cause of a distinct 
odor and taste. 
Jamaica Pond, at Jamaica Plain, Mass., while not a part of any 
water-supply, is interesting, because it illustrates to what an enormous 
extent a member of the Cyanophyceae may multiply in its water, and 
render it unfit for use merely because of the quantity of vegetation it 
contains. In the spring, this pond may be seen to assume a light red- 
dish-brown color. As the season advances the water becomes darker 
and darker until it is of a decided chocolate hue, — certainly not a 
shade which would suggest that it was affected by a “ blue-green ” 
alga. Such is the case, however, for microscopic examination shows 
that the water is filled with the minute filaments of Oscillatoria prolifica 
Gomont. This plant is made up of a series of cells not over 535 mm. 
in diameter, and except for its color presents the usual appearance of 
an oscillatoria. The question as to what gives the cells their chocolate 
color has been the subject of some controversy. Itis not yet definitely 
settled, but it seems probable that the change in hue from blue-green 
to reddish brown is due to the presence of gas vacuoles near the sur- 
(ace of the cells which produce an optical effect sufficient to give the 
chocolate appearance. ‘The reddish-brown color is not an unusual one 
among the CyanopAyceae, it being found in a number of genera besides 
Oscillatoria, one of the most notable examples being that of Z7icho- 
desmium erythraeum Ehrenb., the periodical occurrence of which has 
given the Red Sea its name. 
It was formerly supposed that the minute plants belonging to the 
Diatomaceae, had no injurious effect upon water, and, although they 
are frequently the most common vegetation found in ponds, they were 
passed over as being unimportant. But in recent years it has de- 
veloped that certain diatomes are capable of imparting an oily, vege- 
table taste, while others produce a distinct aromatic odor. Asterion- 
ella, a linear form, inflated at. the ends and usually symmetrically ar- 
ranged in the shape of a star, gives rise to a *'rose-geranium " odor 
which may become fishy as the number of plants increase. There are 
