10 THE ESSEX NATURALIST
The first authentic evidence of this disease, therefore, dates from
one afternoon in the autumn of 1945, when the peculiar appear-
ance of a single sycamore attracted my attention. The tree was
quite dead and was covered from crown to butt with a black to
brown deposit which I at first thought to be decomposed bark.
Subsequent microscopic examination, however, showed the deposit
to be composed entirely of minute fungus spores. It is important
to note that, although this tree was in an advanced state of the
disease and was surrounded by other sycamores, none of these
bore any outward and visible signs of infection. I admit that I did
not make a search as I supposed that the fungus was a harmless
saprophyte, but I was in the area almost daily and I could not
have failed to notice any other similarly affected sycamores.
Thus, two important factors are established. First, that the first
authentic record of the existence of the disease was in the autumn
of 1945, and second, that the single sycamore on which the
disease was first noticed was the focal point of the outbreak as far
as Wanstead Park is concerned.
Our next operation was a survey of every sycamore in the Park,
and as sycamores amount to about forty per cent of the tree popu-
lation of the Park this was a laborious task. However, by the late
spring of 1949 we had accomplished this survey and the results
were disquieting. We located and numbered some 150 sycamores
which bore certain evidence of the disease, namely the sporing
lesions. The advance of the fungi had begun! It must be em-
phasised that all our surveying was done from ground level and it
is important to take into account that the sporing lesions can and
do occur in the top branches where they are not always visible,
even with binoculars.
A study of the map on which the infected trees are marked seems
to show that infection tends to radiate from the position of the
original infected tree. It also seems that the infection has jumped
across the lake at its narrowest part. Here, surely, is strong pre-
sumptive evidence that the spores are dispersed by wind.
As a consequence of our survey the Forestry Commission and
the Epping Forest Conservators were made aware of the dangers
of this fungal parasite and at a conference of these two bodies
means of eradication were discussed. It was agreed that all syca-
mores showing definite signs of the disease should be felled and
burnt on the site. It was not claimed that this would eradicate the
disease but it would certainly lessen spore production and distri-
bution. In the winter of 1949-50, therefore, over 200 sycamores of
all ages, each bearing the characteristic sporing lesions, were felled
and burnt.
It was during this felling that an important contribution to our
knowledge of the disease was made. We had thought that the