i: PITH, OR CENTRE. 5 
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. 1 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 ; 
