they will form a good idea of the formation of the wood. In many of
the specimens there will be knots, and the nature of these will be an
interesting subject for questions. If the knot is near the centre of the
log, lead back their thoughts to the time when the tree was as small as
the annular ring on which the centre of the knot lies. Draw a line on this
ring to represent the tree at this period of its growth. What could the
knot have been? It has concentric circles like the tree itself. It was a
branch which decayed, or was cut off. Year after year, new rings of wood
formed themselves round this broken branch, till it was covered from
sight, and every year left it more deeply buried in the trunk.

Extremely interesting material for the study of wood will be found in thin
sections prepared for veneers. Packages of such sections will be of great
use to the teacher.[1] They show well the reason of the formation of a
dividing line between the wood of successive seasons. In a cross section
of Oak or Chestnut the wood is first very open and porous and then close.
This is owing to the presence of ducts in the wood formed in the spring.
In other woods there are no ducts, or they are evenly distributed, but
the transition from the close autumn wood, consisting of smaller and
more closely packed cells, to the wood of looser texture, formed in the
following spring, makes a line that marks the season's growth.

[Footnote 1: Mr. Romeyn B. Hough, of Lowville, N.Y., will supply a package
of such sections for one dollar. The package will consist of several
different woods, in both cross and vertical section and will contain
enough duplicates for an ordinary class.

He also issues a series of books on woods illustrated by actual and neatly
mounted specimens, showing in each case three distinct views of the grain.
The work is issued in parts, each representing twenty-five species, and