BULLETIN OF THE BUSSEY INSTITUTION. 79 
the Anabena, as a microscopic examination showed no traces of it. 
It would seem then that the peculiar odor, which was so marked in the 
case of Horn Pond, may arise from decay of more than one species 
of the Wostochinee, and the probability is that a large number of spe- 
cies may produce it. The important point is, that it is during their 
decay that the odor is found; not while they are growing. The ques- 
tion arises as to what killed the alge so suddenly. ‘Those living near 
the pond are quite ready to believe that it was the refuse from the 
tanneries, but there is no proof whatever that that was of a different 
character from what it had been previously, and the question is still 
open, why at that particular time the alge were killed. It will be 
remembered that, during the month of August, 1876, the heat was 
excessive, and the temperature of the surface water was raised con- 
siderably. We cannot doubt that the broiling rays of the sun had 
a destructive effect on the Anabena, especially that which was 
caught in the meshes of the Plectonema, and, by the falling of the 
water consequent upon the drought, exposed on the surface. 
From the preceding account of the condition of Horn Pond, we are 
warranted in drawing certain conclusions which may on some occasion 
prove useful to water boards. If a sudden odor of pig-pen arises, it is 
in all probability owing to the decay of large quantities of some algz 
of the nostoc family, and most probably one of the finer species 
diffused through the water. As the decay is generally, if not always, 
brought about by causes beyond human control, it is useless to try to 
stop it when it has once begun. On the other hand, there is no occa- 
sion for great alarm; for, when they have once begun to decay, alge 
like Anabena disappear in a few days. In the case of Horn Pond, 
we understand that the odor lasted barely a week from the time when 
it was first perceptible. As to the possibility of the putrescent masses 
being carried any great distance, in the case of Horn Pond it was 
found that they advanced as far as Winchester, not more than two 
miles in a direct course, but were not found farther on. ‘They never 
made their appearance in Charlestown or East Boston. Knowing 
that floating algz are caught in the meshes of Plectonema and other 
similar filamentous alge, and thus, during the sinking of the water, 
which usually occurs in July and August, exposed on the surface to 
the direct heat of the sun’s rays, which cause them to decompose, it is 
evident that it is a useful precaution to remove, as far as possible, the 
