Series editors' preface - Wood Tools

about the same size as the width of a cotton
fibre, or of a very large bacterial cell.
Fungi have two basic kinds of structures,
specialized for growth and for reproduction.
The vegetative structure responsible for
growth is the threadlike filament called the
hypha. Collectively, hyphae are referred to as
the mycelium. The diameter of the hyphae
varies considerably but mostly falls in the
range 2–20 μm. The principal reproductive
unit is the spore. The relationship between the
spores and the hyphae varies. In the simplest
cases, the spore is formed from cells of the
hyphae that separate at maturity. In other
cases, more complex relationships exist.
Spores may arise for example from specialized
stalks or branches borne by the hyphae rather
than directly from the hyphae themselves.
Spores may be of two types. Under ideal
growing conditions a type of spore may be
formed rapidly and in large numbers that is
suitable for rapid multiplication but has little
resistance to adverse conditions. Another type
of spore, suited to tiding the organism over
periods unfavourable for growth, is produced
under appropriate conditions. These may live
for many years and can become widely distributed.
Some of the fungi that cause deterioration
reproduce by sexual methods while
others do so asexually.
Control of fungi Factors that influence the
growth of fungi include temperature, humidity,
light, oxygen and the food source. The
temperature range inhabited by various different
fungi goes from just above freezing to
about 50 °C. For each species there is a
preferred temperature range at which growth
rate is optimum, a temperature below which
growth will not occur and a temperature
above which growth will not occur. The
optimum for many fungi lies in the range
15–30 °C. Many fungi will survive continuous
freezing for several months but are less tolerant
of repeated freeze–thaw cycles. Moist heat
kills them more readily than dry heat. The
critical average moisture content of a material
for fungal growth is 20%. The corresponding
RH is unlikely to be much below 70%. In
conditions much drier than this fungi will not
grow. Most fungi require a supply a supply of
oxygen for growth but will operate independently
of lighting conditions, although they
General review of environment and deterioration 267
may be damaged or killed by UV radiation.
Fungi require sources of carbon, hydrogen,
oxygen, nitrogen, sulphur, potassium, magnesium
and phosphorous for growth. They may
also require traces of iron, zinc, copper,
calcium and manganese. Many naturally occurring
compounds may be used by fungi as a
source of carbon and energy. Glucose,
sucrose, animal and vegetable fats and their
component acids and glycerine can generally
be used and some, but not all, fungi are able
to utilize cellulose. Nitrogen may be assimilated
as nitrates, ammonium salts, amino acids
or proteins. Since the absence of any of these
requirements will prevent or greatly inhibit
growth, methods for control are based on
eliminating or modifying one or more of these
conditions by keeping objects clean and under
suitable conditions of RH. Alternatively,
poison, as used in wood preservatives, offers
an effective and reliable means of protection
in high risk situations. Methods of controlling
fungal problems are further discussed by
Strang and Dawson in Canadian Conservation
Institute Technical Bulletin No. 12.
The chief products of fungal metabolism are
carbon dioxide and water. However, other
products are also formed that themselves have
a deleterious effect on objects. These include
various organic acids, alcohols and esters. The
formation of coloured material is also
frequently conspicuous.
Insects
All insects are members of the class Insecta
belonging to the vast phylum Arthropoda, the
most complex and specialized group of invertebrates
in the animal kingdom. About one
million different insect species have been
recorded to date though no one really knows
how many species there are on the earth
today. Between them, insects will eat virtually
anything organic, including many of the
materials used in the construction of furniture
and wooden objects. They may also cause
incidental damage, for example by their
excreta. This causes them to be regarded as
pests and for man to seek to eliminate them
at least from environments in which valuable
furniture is being maintained. Insect damage
needs to be understood in relation to the
habits of insects, their life cycle, the nature
and distribution of the collections and the