284 THE ESSEX NATURALIST.
with a growth of green autotrophic flagellates, now ready to
take advantage of the penetrable tissues of the enfeebled hosts
in their demand for a benthic substratum." The green flagel-
lates supply the place of the original green film of the surface
layers, and thus the tissues of the denuded central axis are able
to continue their metabolism at the expense of the waste carbo-
hydrate and liberated oxygen that is available in the vicinity of
the newly acquired green autotrophic cells.
It is evident from what has already been said, that the greater
number of papers on lichen ecology consists of those relating to
the sea-coast. It is possible that this is so because such
localities are more accessible than high mountain summits, which
need to be visited frequently if effective work is to be accom-
plished, for the greater part of the observation can only be
carried out while the lichens are in situ.
Contributions to our knowledge of the ecology of the lichens
of lowland woods have not been forthcoming to any great extent.
It would appear that an increasing number of botanists are
being attracted to the subject of lichens ; but the scarcity of
reliable guides, both for field work and for the laboratory, has
militated against the pursuit of Lichenology in this country.
We can, however, now look forward, to meet this want, to the two
volumes that are announced as in the press, both of them by
Miss A. Lorrain Smith, one being a volume of the "Cambridge
Botanical Handbooks" and the other a book for field work,
somewhat similar in size and volume to "Hayward's Botanist's
Pocket Book." It may here be noted that photo-micrography
has been recently employed, for the first time in this country,
for illustrating papers dealing with lichen symbiosis and
lichen spores.
I take this opportunity of thanking Professor F. W. Oliver
for lending me lantern slides and specimens for exhibition, and
Mr. J. H. Pledge for the very valuable help he has given me
in making photo-micrographs, from my preparations.
BIBLIOGRAPHICAL SUMMARY.
The titles of papers are arranged in sections according to
the chief feature of the contents, and also in chronological order,
except when more than one paper by the same writer has to be