look for the pith or centre of the stem, or—if that has been removed by the conversion of the tree—for the innermost, or oldest layer of heart-wood, in the plank or board, as that will be the inside of it. If this precaution is disregarded, the innermost or
FIG. I.
earlier layers of wood lift and shell out, after exposure for a time, in shreds and strips, the cohesive properties of the ligneous layers having been destroyed by the action of the atmosphere. Fig. I shows the plank properly fixed, with the inner or earlier layers of wood
FIG. 2.
against the beam, in which position it is impossible for them to separate. Fig. 2 shows the plank improperly fixed, with the outer, or later layers of wood against the beam, in which position the earlier layers are very liable to lift, or shell out, destroying the evenness of surface;
