FIELD PHENOMENA DUE TO MICROSCOPIC ORGANISMS. 13
in the lane, and the small branches were burnt on the spot. Three
more or less circular areas of white ash, from 7-8 feet across and
some distance apart, remained on the ground, and each of these
showed the greater part covered with a very thin layer of what
appeared to be a red pigment varying in tint from a bright salmon
colour to a dull brick-red. This layer, when examined, was
found to be due to innumerable spherical bodies about 1/3,000" in
diameter, of a beautiful golden red colour, which were evidently
resting stages (akinetes) of some unicellular alga. From the
evidence of a small number of greenish cells mixed in parts with
the red cells, it seems probable that the organism concerned was
a species of Chlorococcum. The case is a very interesting one, as
it opens up a number of questions as to how the alga reached the
three separate patches of burnt wood ash, how it spread over
the surface so nearly uniformly, and also as to the influence of
the peculiar sub-stratum itself upon the production of the resting-
cells. Efforts to cultivate the material have not so far yielded
any definite results, but it is hoped to continue this work. In a
week or so after the red colour was first noticed the surface of the
ash commenced to turn a greenish tint. This was brought about
by the development of moss protonema, and now the burnt areas
are almost entirely carpeted with mosses.
Purple or pinkish-purple patches on the ground, often
covering considerable areas, are well known to all who have
tramped over Dartmoor and many other heaths and moors. They
are produced by a felt-like growth of filaments of the alga
Zygogonium ericetorum, a plant very closely allied to the wholly
aquatic Zygnema. Although a typically green alga, it frequently
develops when drying the colouring matter known as phycopor-
phyrin in its cell-sap, especially if growing on peaty soils. The
sheets of matted threads which it forms on the ground are
believed to act in a beneficial way to some of the smaller flowering
plants, such as Drosera, when growing round them, by absorbing
water whenever possible and also by protecting the surface of
the soil from too rapid drying during periods of drought. In this
district I have seen it forming dark green patches on bare
ground under trees, and also giving a dull purple colour to small
pieces of open ground on Leyton Flats and near Strawberry Hill,
and no doubt it occurs in many other parts of the Epping Forest
area. Prof. Fritsch has put on record some important observa-