14
THE ESSEX NATURALIST
Everhart, 1889. In November 1950 I wrote to Dr. John Dearness,
the veteran Canadian mycologist, who collected the type material,
asking if he could give further information on the occurrence and
status of the fungus. In his reply, written in his ninety-ninth year,
Dr. Dearness said, "I made the type collection on four-foot long
cuttings of a load of maple bought from a farmer living about ten
miles from London, Ont. The trees would be about eight to twelve
inches in diameter, probably felled in the winter of 1888 or 1887
and delivered to me for firewood in 1889." The maple used for
firewood was probably Acer saccharum. Since the time of Dear-
ness's original collections the fungus has been reported only
twice, once from Michigan and once from Wisconsin.
A comparison of specimens established the specific epithet
corticale for the Wanstead sycamore fungus, but did not place it
in a satisfactory genus. Although keys to the Fungi imperfecti at
present in use give Coniosporium as having dark, non-septate
spores like the sycamore fungus, the genus Coniosporium Link is
now known to be based on a species with large multi-septate
spores. Further, the structure of the sycamore fungus is distinctive
and does not fit conveniently into any genus yet described. We
have therefore erected the new genus Cryptostroma Gregory and
Waller (Hyphomycetes, Dematiaceae), to which we have trans-
ferred Coniosporium corticale Ellis and Everhart as the type species.
Cryptostroma corticale invades the cambium, bast, and to some
extent the medullary rays of the wood. In its sporing phase the
fungus forms a compact sheet of hyphae which splits the bark into
two layers. The lesions may be small, or they may girdle the tree
so that all the outer bark is shed for many feet up the trunk.
Where a stromatic layer is formed the bark is forced apart as an
inner and outer layer at first held together by the fungus itself.
In its sporing stage the fungus consists of two flat sheets of
hyphae compacted into a stroma, the inner one called the floor
stroma on which stand numerous black columns raising the outer,
roof stroma to perhaps as much as a millimetre above the floor.
The spores are produced from a layer of short conidiophores
which cover the floor stroma, like the pile of a carpet (Fig. 1).
From the ends of the conidiophores brown, smooth, ovoid spores,
5.4μ. x 3.9μ., are produced in fragile chains, and the space between
the floor and the roof is filled with the dry, powdery mass of
spores. Delicate unbranched threads attached to the floor stroma
penetrate the spore mass.
At maturity the columns break across and the outer bark and
roof stroma peel off, exposing the spore layer to the air where the
spores can be removed freely by the wind. With its outer bark re-
moved the tree is conspicuous because of the velvety, brown to
black spore layer on dead parts of the trunk and branches.