age of
only 7 per cent in volume, based on the green dimensions, in the case
of some of the cedars to nearly 50 per cent in the case of some
species of eucalyptus.

When the free water in the capillary spaces of the wood fibre is
evaporated it follows the laws of evaporation from capillary spaces,
except that the passages are not all free passages, and much of the
water has to pass out by a process of transfusion through the moist
cell walls. These cell walls in the green wood completely surround the
cell cavities so that there are no openings large enough to offer a
passage to water or air.

The well-known "pits" in the cell walls extend through the secondary
thickening only, and not through the primary walls. This statement
applies to the tracheids and parenchyma cells in the conifer
(gymnosperms), and to the tracheids, parenchyma cells, and the wood
fibres in the broad-leaved trees (angiosperms); the vessels in the
latter, however, form open passages except when clogged by ingrowth
called tyloses, and the resin canals in the former sometimes form
occasional openings.

By heating the wood above the boiling point, corresponding to the
external pressure, the free water passes through the cell walls more
readily.

To remove the moisture from the wood substance requires heat in
addition to the latent heat of evaporation, because the molecules of
moisture are so intimately associated with the molecules, minute
particles composing the wood, that energy is required to separate them
therefrom.

Carefully conducted experiments show this to be from 16.6 to 19.6
calories per grain of dry wood in the case of beech, long-leaf pine,
and sugar maple.

The difficulty imposed in drying, however, is not so much the
additional heat required as it is in the rate at which the water
transfuses through the solid wood.

SECTION VIII

ADVANTAGES IN SEASONING

Three most important advantages of seasoning have already been made
apparent:

1. Seasoned timber lasts much longer than unseasoned. Since
the decay of timber is due to the attacks of wood-destroying
fungi, and since the most important condition of the growth
of these fungi is water, anything which lessens the amount
of water in wood aids in its preservation.

2. In the case of treated timber, seasoning before treatment
greatly increases the effectiveness of the ordinary metho