FIELD PHENOMENA DUE TO MICROSCOPIC ORGANISMS. 17
several kinds of Sulphur Bacteria such as Chromatium, Lampro-
cystis, etc., and occasionally by Entomostraca, more particularly
certain species of Daphnia, such as D. pulex and D. obtusa. A very
striking case of the Water of a pond in Epping Forest being turned
so red by Chromatium Okenii as to appear almost like blood was
the subject of a short article by me in the Essex Naturalist
last year.
Blue or bluish-green water has been recorded as being due
to the spores of one of the blue-green algae, Anabolia Lemmer-
manni, and the marginal waters of a pond have been seen to be
so thickly populated by a species of the ciliate Steutor(S. niger),
that they appeared nearly black.
One of the most curious examples of the coloration of water
that I have myself noticed occurred in the pond at Fairmead
in which the previously mentioned Chromatium had been found
so abundantly. After the Chromatium had "gone off colour,"
so to speak, the water became nearly white, somewhat the colour
of dirty milk, and this was found to be due to excessively minute
highly refractive bodies, on an average only about 1/50,000" in
diameter. What these were it is not possible to say with cer-
tainty, but they appeared to be exactly the same as the spores
which were to be seen inside a number of bacteria (Spirillum,
etc.), which were also present in the water in small numbers. It
would be a very remarkable fact if it could be definitely shown
that a whole pond could be turned into a sort of milk through the
liberated spores of bacteria, and one giving rise to many inter-
esting speculations.
A second category of aquatic phenomena due to microscopic
organisms is that in which the water is turned into a sort of thin
flocculent paste of an orange or rusty-red colour. This appear-
ance is more usually met with in what are known as "iron-
springs," of which there are several in the Epping Forest district,
and it is due to the abundant development of certain "iron-
bacteria." These are filamentous bacteria, which possess the
power of depositing an oxide of iron in the sheaths with which
they are usually surrounded. The form which most frequently
causes the phenomenon of the "iron-springs" is Leptothrix
ochracea, but a number of other iron-bacteria such as Gallionella
ferruginea, Spirophvllum ferrugineum, etc., are usually associated
with it.
B