12 THE ESSEX NATURALIST
was imported there? The history of fungus epidemics contains
cases of species which, although harmless saprophytes in their
place of origin, became virulent parasites when transported to a
new clime and a different host. The Endothia blight of the chest-
nut, which is slowly and steadily wiping out the chestnut in the
U.S.A., was imported there from Japan.
On the completion of the survey the Forestry Commission was
in possession of enough information to recognise the importance
and the potentialities of the outbreak at Wanstead and they acted
accordingly. In January 1950 a meeting, attended by several plant
pathologists, was held in London. The purpose was to discuss the
Wanstead fungus and to formulate plans to combat its ravages.
It was decided (1) to appoint two surveyors to tour the whole
country if possible in an intensive search for the disease, and (2) to
appoint a research worker to study the life-history of the disease.
The interim report of the surveyors is to hand and it shows a
marked increase in the area affected. The survey is still continuing.
There is an important aspect of these surveys which should be
clearly recognised, and that is that the results and figures shown
relate only to positive indications—i.e., the sporing lesions—dis-
covered. As I have already pointed out, the sporing lesions are a
late phase of the disease and they do not appear until it is well ad-
vanced. Thus a tree classified as healthy one week may be sporing
the next week, so that if these surveys are to be effective they must
be repeated at intervals. I should also like to point out that in
mature rough-barked sycamores, where the bark has been harden-
ed and split by age, frost, etc., the fungus has great difficulty in spor-
ing. We have met with cases where sycamores have undoubtedly
been killed by the fungus which has not succeeded in sporing at all.
In Wanstead Park Dr. Gregory and I have for the past two years
made intensive observations of the sycamores, and the position
today still causes some anxiety. From all our observations and de-
ductions there can be no doubt that the Park is the focus of the
disease. Although over 200 diseased sycamores have been felled
and burnt, yet within a year there are today just as many more
dead and dying victims to this parasite. Although the sycamore is
not a native of this country it is a comparatively healthy tree and
with the exception of Gnomonia veneta—a leaf and twig parasite—
and Rhytisma acerinum, which causes the familiar black blotches
on the leaves, it was practically immune from fungus disease until
it met with the Wanstead parasite. It may be that this fungus will
depart, leaving behind a trail of devastation, but it may well be
that we are witnessing the beginning of the end of sycamores in
this country. It is a matter of history that the Coffee Rust (Hemi-
leia vastatrix) destroyed the coffee industry in Ceylon.
I have refrained from dealing with the morphology of this