Introduction to Fungi, Third Edition

BOLETOID CLADE
559
such timbers that the fungus is most frequently
reported. There is evidence that S. lacrymans
has become adapted to man-made habitats.
In the wild, S. lacrymans has been collected
on spruce logs in the Himalayas at an altitude
of 8000 10 000 ft (Bagchee, 1954; Singh et al.,
1993), and it has also been reported from
Northern Europe, Northern California and
Siberia. It can continue to grow vegetatively at
2°C, and the optimum (23°C) and maximum
(26°C) temperatures for growth are rather low.
Strains of S. lacrymans associated with houses
are considered to belong to S. lacrymans var.
domesticus and may have been spread by human
activities in recent times. The Himalayas are
often mentioned as a likely centre of origin,
although Kauserud et al. (2004) put forward an
alternative hypothesis featuring North America.
Either way, possible vehicles for the dispersal
of S. lacrymans var. domesticus may have been
wooden sailing ships. Ramsbottom (1938),
in his fascinating review of a wealth of original
literature sources, concluded that wooden
vessels were frequently infested by S. lacrymans,
often being unsound even before being launched
due to the careless use of non-seasoned
timber combined with poor ventilation of the
ship holds. Typical symptoms were described by
a Commission of Inquiry, reporting to King
James I in 1609 on the state of battleships in
the Royal Navy (taken from Ramsbottom, 1938):
In buylding and repaireing Shippes with greene
Tymber, Planck and Trennels it is apparent both by
demonstration to the Shippes danger and by heate of
the Houlde meeting with the greenesse and sappines
thereof doth immediately putrefie the same and
drawes that Shippe to the Dock agayne for
reparation within the space of six or seven yeares
that would last twentie if it were seasoned as it
ought and in all other partes of the world is
accustomed. Adde hereunto experience at this day
that many Shippes thus brought in to be repaired,
subject to miscareinge upon employment, and
besides they breed infection among the men that
serve in them.
Only wood with a moisture content above about
20 25% of the oven-dry weight is susceptible to
attack by the fungus. Well-dried and seasoned
timber has a moisture content of 15 18%, and
in a properly ventilated house this soon falls to
12 14% or lower. If woodwork becomes wet
through contact with the soil, damp masonry,
faulty construction or inadequate ventilation,
then infection from air-borne basidiospores is
likely to follow. Basidiospores germinate in the
presence of free water on moist wood surfaces.
The mycelium within the wood develops chiefly
at the expense of the cellulose; lignin is not
attacked, and the type of decay is a brown-rot.
Well-rotted timber is shrunken with transverse
cracks and has a dry crumbly texture.
Water produced by the breakdown of cellulose
(sometimes termed the water of metabolism)
may be sufficient for further growth even if the
air humidity is lowered below the point at which
new basidiospore infections could arise. Up to
55.6% of the cellulose consumed may be available
as metabolic water (see Bravery, 1991). As in
many brown-rot fungi (see p. 527), oxalic acid is
released into the environment, lowering the pH
of the wood and mortar over which S. lacrymans
is growing.
The epithet lacrymans (weeping) refers to the
beads of moisture sometimes found on decaying
timber, at the tips of hyphae and on mycelial
cords. Sheets of mycelium may extend over the
timber and adjacent brickwork, and the fungus
is also capable of spreading several metres by
means of mycelial cords up to 5 mm in diameter.
The internal hyphae of the mycelial cords
are exceptionally wide (up to 60 mm) and are
modified for rapid conduction, enabling water
and nutrients to be transported (Nuss et al., 1991).
Transport is by pressure-driven hydraulic flow
(Jennings, 1987, 1991). Carbohydrate is transported
mainly in the form of trehalose.
The strands can penetrate mortar and stonework
between walls and can spread throughout a
building provided that there is enough wood as
a food base. Strands remaining after removal
of affected timber may still be able to initiate
fresh infections.
Reproduction in Serpula lacrymans
This fungus is heterothallic and tetrapolar.
Globally there are probably no more than four
A and five B alleles (Schmidt & Moreth-Kebernik,
1991). Arthroconidia are formed on