38 THE ESSEX NATURALIST.
are radial sheets of tissue : if a section be cut longitudinally
along a ray, i.e., a radial section, the ray will appear as a silvery
streak: a board cut in such a manner is termed quarter-
sawn, and will show the greatest amount of silver grain. A
section cut longitudinally at right angles to the ray will obviously
show the smallest area of ray, the ray appearing as a thin
fusiform streak, up to about a couple of inches long, at most ;
such a section is termed tangential, and planks cut so that their
faces are tangential surfaces are referred to as plain sawn.
Examination of the end of the log with the lens will reveal that
the annual rings are made prominent by rings of large pores;
these are the cut ends of vessels, which are the main conducting
elements of the wood: they are laid down each spring. The
spring wood contains other elements as well, but the bulk of it
consists of these vessels. The later formed wood, usually
referred to as the autumn wood, but more appropriately as the
summer wood, contains relatively few small vessels running in
radial lines : the remainder of the wood consists of fusiform
fibres, which are the supporting elements, tracheids, which,
like the vessels, are conducting elements, and somewhat brick-
shaped parenchyma cells, which are the only living elements
of the wood. In oak these parenchyma cells are associated
with the vessels of the summer wood, and also in tangential
lines connecting adjacent rays. The lens also shows numerous
small rays between the larger ones. Not all the wood functions
as a water conducting tissue ; this is the work of the sapwood ;
the heartwood is a dead supporting tissue ; its cells and vessels
become impregnated with waste substances like tannin and it
is these which give the wood its dark colour. In many trees
there is no visible heartwood, the wood from pith to bark being
uniform in colour ; such trees, e.g., Hornbeam, are termed sap-
wood trees, but this term is misleading, for in these trees as in
heartwood trees the more central wood does not conduct water
and should therefore be called heartwood.
The end grain of a piece of Beech presents a different appear-
ance. Rays are visible, but the larger ones are much smaller
than in oak; the annual rings are less conspicuous, and dip
inwards where they cross the large rays. The lens will reveal
the vessels, much smaller than those in the spring wood of oak,
and varying but little in size throughout the season's growth.