(See Fig.

21.) The plane of cleavage is parallel to the grain, either radially or tangentially.
[Illustration: FIG.

21 .-- Cleavage of highly elastic wood.

The cleft runs far ahead of the wedge.] This property of wood is very important in certain uses such as firewood, fence rails, billets, and squares.

Resistance to splitting or low cleavability is desirable where wood must hold nails or screws, as in box-making.