FUNGUS DISEASE OF SYCAMORE 11
sporing lesions denoted points of infection from without, but sub-
sequent examination of felled sycamores showed that such was
not the case. Every tree felled showed in transverse section a
significant area of dark brown stain bordered by a narrow black
zone. Dr. Gregory will deal with the implications of this stain in
detail but I should like to emphasise the serious problem created
by the discovery of this internal symptom. The stain undoubtedly
indicates the presence of the disease in the tree, while the sporing
lesions indicate a much later phase of the disease. The disease,
therefore, spreads internally and this means that sycamores can
be infected without showing any external symptoms whatsoever.
This discovery makes eradication measures extremely difficult, if
not impossible. How can the ravages of this fungus be combated
when there are no external symptoms until the disease is so far
advanced that it is too late to save the tree?
I have previously mentioned that this fungus exhibited novel
and distinctive features. The chief of these is, in my opinion, its
phenomenal sporing capacity. A mature sycamore may be clothed
entirely from crown to butt with a dark brown to black stratum,
fully l/8in. thick, composed entirely of minute fungus spores.
When the spore mass is mature it is a common sight to see the
surrounding vegetation blackened by the dispersed spores. It
would be too much to hope for or to imagine that this fungus,
with its almost unlimited sporing capacity and power of repro-
duction, could be confined within the boundaries of Wanstead
Park. The Forestry Commission, recognising the danger of the
disease spreading all over the country, consequently appointed a
surveyor to make an intensive and extensive tour of certain areas
of London and the suburbs.
This survey consisted of (1) an intensive street by street search
in the immediate vicinity of Wanstead Park; (2) an extensive
search over a fifteen-mile radius from Wanstead Park; (3) a
circular tour of about twenty miles around the outskirts of
London.
The results of this survey were very interesting. As expected,
numerous isolated outbreaks of the disease were found; most of
these were in the vicinity of the Park. In all the survey, however,
no large areas of the disease comparable to that at Wanstead
were found. The area of infection was roughly in the shape of a
triangle with Plumstead to the south, Hampstead to the north, and
Claybury to the east. The outbreaks found at Plumstead and
Plaistow were extremely interesting and may afford a solution to
the problem of whence came this disease. Both Plumstead and
Plaistow are heavily built-up areas on opposite sides of the
Thames; between them lie the docks and here a considerable im-
port trade in timber is done. Can it be that the Wanstead fungus