PAINTING MATERIALS

5. Rays (medullary rays). These may be observed as radiating lines in the
cross section of a tree. The rays serve the tree for purposes of conduction and
storage. They are particularly conspicuous in oak, beech, and button-wood. The
ways in which logs are cut up are described with reference to their relation to the
position of the rays and also to the rings. Quarter-sawed, edge-grained, or radially-
cut lumber is sawed parallel with the rays. Plain-sawed, flat-grained, or tangen-
tially-cut lumber is sawed at right angles to the rays.

Transverse Section <ss5>-

$ Tangential Sectton

'Cowpoxmct Ray

•Zonate Diffuse,
Parenchyma

with

ScaTaraform Openinq
OJnlsertat* Ray **

FIGURE 3. A block section of beech-wood, at about 200 diameters, adapted from figure
12, page 39, of 'Technology of New York State Timbers/ Technical Publication no. /<£,
New York State College of Forestry (Syracuse University, 1926), by C. C. Forsaith.
Apart from these characteristics, all woods may be divided into two main
groups: hard-woods and soft-woods or conifers. The two classes differ in structure
and not in the literal meaning of the terms, * hard ' and * soft.'
i. Hard-woods are structurally more complex than soft-woods. They all have
a certain type of cell, larger than the others, which is called a * pore ' or * vessel*.
The pores are specialized for sap conduction and have open ends. They are fused
together, end to end, and, when not closed by tylosis, they aid in the drying of a
wood or in impregnating it with a preservative. Hard-woods are subdivided into
two groups, based upon the arrangement of the pores. The first is ring-porous
hard-wood, e.g*y oak, ash, elm. These have comparatively large spring-wood
pores which are generally visible to the naked eye. On the end grain of a log the
pores form distinct rings and there is a marked difference between the size of the
spring-wood pores and those of summer-wood. The second group comprises the
diffuse porous hard-woods, e.g., maple, black walnut, yellow poplar. The pores,