288 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
sixteen of the spruce trees. A strict comparison of the relative 
properties of these two species was thus rendered possible, and 
this constituted an important detail of the inquiry. 
In the case of the silver fir the heaviest timber was found 
in the lowest section of the stem, a gradual fall in the sp. gr. 
occurring as the bole was followed up to the crown. 
As regards age, it was found that the older the tree the heavier 
the timber (sp. gr.=°395 for a tree 30 years old, ‘416 for a tree 
120 years old). Where sections of trees 120 years old were 
examined, the lightest timber was got near the centre (395), the 
sp. gr. gradually rising as the periphery was approached (-424). 
The shrinkage was found to decrease slightly as the stem was 
followed towards the crown (12°1 % at 1 metre, 11:5 Y% at 17 
metres), while it increased as the periphery of a section was 
approached (10°8 % within the 3lst ring, 12:1 {%{ between the 
90th and 121st rings). The average per cent. of shrinkage for 
whole stems is put at 11°8. 
Resistance to pressure agreed closely with the sp. gr, Thus, 
timber taken 4 metres or less from the ground withstood crushing 
better than timber situated higher up. 
The limits of variation in sp. gr. in nie case of the silver fir 
were found to be :— 
(a) For definite periods of growth, . ‘488 and ‘315. 
(6) For whole sections, : : . ‘477 and °354. 
The limits of variation of resistance to pressure in lbs. per — 
square inch of cross section were 8300 and 3915, 
As an average for the whole stem of a mature tree, Prof. 
Schwappach suggests :— 
Sp. gr. = 410. 
Resistance to pressure = 5675. 
These figures indicate a lower technical quality for Thuringian 
silver fir than for ordinary spruce. 
LV. Witu tHE Weymouts PIne. 
The trees of this species submitted to investigation came from 
two plantations, about 100 years old, situated in Silesia. 
As in the case of the Scotch fir, the highest sp. gr. was found 
in the lowest section of the stem (‘391 at 1 metre, °370 at 12 
