280 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
determinations, while those marked a, b, ¢ were designed to 
be used for ascertaining the specific gravity. The portions to 
be used for determining the pressure were square on section, 
and, the side of the square having been ascertained, the stem 
was cut through at that distance from the first section, so 
that, when the shaded portions were ultimately sawn out in the 
laboratory, they formed true cubes. Seeing that the radius of the 
stem at any section was always taken as the length of the diagonal 
of the surface of the cube, the dimensions of the cube were always 
in direct relationship to the thickness of the tree. The portions 
of timber with which the specific gravity was determined always 
corresponded to periods of growth of 30 years each; that is to 
say, @ would comprise the wood formed before the 31st year, 
b the wood formed during the period from the beginning of the 
31st to the end of the 60th years, and so on. This plan was 
first suggested by Prof. R, Hartig, and is now generally adopted 
in investigations similar to those under discussion. Evaporation of 
moisture between the forest and the laboratory was largely avoided 
by coating the sections with vaseline, and packing them in parch- 
ment paper. Before testing for shrinkage, the wood was steeped 
for 48 hours in water, so that its original volume was restored. 
