STEMS AND BRANCHES 12 
these are the silver grain ; they are called by the botanist 
medullary rays. 
The central portion of the wood of many large stems is 
darker in color than the rest. This darker portion is dead 
wood, and is called heart-wood ; the outer portion, called 
sap-wood, is used in carrying the sap during the growing 
season. The heart-wood of the Walnut-tree is very dark 
brown; that of the Cherry, light red; and that of the 
Holly, white and ivory-like. The heart-wood is the valu- 
able part for lumber. : 
If examined under a magnifying glass, the annual layers 
will be seen to consist of minute tubes or cells. In most 
trees these tubes are much larger in the portion that grew 
early in the season, while the wood seems almost solid 
near the close of the annual layer; this is especially true 
in the Ashes and the Chestnut; some trees, however, show 
but little change in the size of the cells, the Beech being 
a good example. In a cross-section, the age of such trees 
as the Chestnut can readily be estimated, while in the 
Beech it is quite difficult to do this. Boxwood, changing 
least in the character of its structure, is the one always 
used for first-grade wood-engravings. 
When wood is cut in the direction of the silver grain, 
or cut “ quartering” as it is called by the lumbermen, the 
surface shows this cellular material spread out in strange 
blotches characteristic of the different kinds of wood. 
Fig. 16 shows an Oak where the blotches of medullary 
rays are large. In the Beech the blotches are smaller; 
in the Elm quite small. Lumber cut carefully in this 
way is said to be “ quartered,” and with most species its 
beauty is thereby much increased. 
Any one who studies the matter carefully can become 
acquainted with all the useful and ornamental woods 
used in a region; the differences in the color of the heart- 
wood, the character of the annual layers, and the size and 
the distribution of the medullary rays, afford enough 
peculiarities to distinguish any one from all others. 
