ber after it is
placed in the buildings. They are particularly to be dreaded
because unseen, working as they do within the walls or inside of
casings. Several serious wrecks of large buildings have been
attributed to this cause. It is stated[40] that in the three
years (1911-1913) more than $100,000 was required to repair
damage due to dry rot.

[Footnote 40: Dry rot in factory timbers, by Inspection Dept.
Associated Factory Mutual Fire Insurance Cos., 31 Milk Street,
Boston, 1913.]

Dry rot develops best at 75 deg.F. and is said to be killed by a
temperature of 110 deg.F.[41] Fully 70 per cent humidity is
necessary in the air in which a timber is surrounded for the
growth of this fungus, and probably the wood must be quite near
its fibre saturation condition. Nevertheless _Merulius
lacrymans_ (one of the most important species) has been found to
live four years and eight months in a dry condition.[42]
Thorough kiln-drying will kill this fungus, but will not prevent
its redevelopment. Antiseptic treatment, such as creosoting, is
the best prevention.

[Footnote 41: Falck, Richard: Die Meruliusfauele des Bauholzes,
Hausschwammforschungen, 6. Heft., Jena, 1912.]

[Footnote 42: Mez, Carl: Der Hausschwamm. Dresden, 1908, p. 63.]

All fungi require moisture and air[43] for their growth.
Deprived of either of these the fungus dies or ceases to
develop. Just what degree of moisture in wood is necessary for
the "dry-rot" fungus has not been determined, but it is
evidently considerably above that of thoroughly air-dry timber,
probably more than 15 per cent moisture. Hence the importance of
free circulation of air about all timbers in a building.

[Footnote 43: A culture of fungus placed in a glass jar and the
air pumped out ceases to grow, but will start again as soon as
oxygen is admitted.]

Warmth is also conducive to the growth of fungi, the most
favorable temperature being about 90 deg.F. They cannot grow in
extreme cold, although no degree of cold such as occurs
naturally will kill them. On the other hand, high temperature
will kill them, but the spores may survive even the boiling
temperature. Mould fungus has been observed to develop rapidly
at 130 deg.F. in a dry kiln in moist air, a condition under which an
animal cannot live more than a few minutes. This fungus was
killed, however, at about 140 deg. or 145 deg.F.[44]

[Footnote 44: Experiments in kiln-drying _Eucalyptus_ in
Berkeley, U.S. Forest Service.]