16
THE ESSEX NATURALIST.
ducing a green coloration in water are various species of Euglena
and Chlamydomonas and less frequently Volvox.
The number of other organisms which occasionally, either by
themselves or in company with others, turn water green is so
large that it is quite impossible to refer to them in detail here,
and it must suffice to say that they include species of Gonium,
Eudorina, Scenedesmus, Ankistrodesmus, Selenastrum, Pediastrum,
Chlorella, etc. There is one species, however, of this miscel-
laneous class, to which a little attention may be given, as it
illustrates very well the way in which a comparatively rare form
may, under suitable conditions, become absolutely dominant in
a piece of water. It also has a certain interest for us as Essex
naturalists, in that it was first found in the Epping Forest
district, and was not only a species new to science, but the type
of a new genus. In the early part (end of January) of 1912 I
noticed that a pond on Leyton Flats was distinctly green in
colour, and I found that the colour was entirely due to myriads
of a very small biflagellate organism, only about 1/4000" in
length, which, although evidently allied to Chlamydomonas, I
was unable to place in any genus known to me. Prof. G. S. West,
to whom specimens were sent, described it later in the Journal
of Botany under the name of Scourfieldia complanata. From our
present point of view the most remarkable thing about it was
that the pond in question remained in the same green condition
for nearly three months, including one spell of sharp frost when
the pond was covered with ice, and during all this time the colour
was due to this one species, and nothing else, as there were very
few other organisms present, and none in appreciable numbers.
A golden-brown colour of the water may be brought about
by a number of different organisms, but they are not so numerous
as the green forms. This colour is due either to Chrysomonads,
such as Synura, or to Cryptomonads, such as Cryptomonas, etc.,
or to Dinoflagellates such as Peridinium, Ceralium, etc. Occa-
sionally it is caused by a peculiar green alga, Botryococcus Braunii,
which is usually yellow, yellow-brown, or even red, rather than
green, owing to the production in large quantities of a coloured
oil.
Red, or even blood-like water, may also be produced by
quite a number of distinct organisms. The chief of these are one
or two species of Euglena, such as E, sanguinea and E. haematodes,