286 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
“ And further :— 
“4, For any definite sp. gr. the cell-walls do not exhibit 
uniform rigidity.” 
The limits of variation in the sp. gr. determinations of air-dry 
specimens of Scotch fir were found to be :— 
(a) In the case of definite periods of growth, from ‘778 to 
‘299, so that a cubic foot might weigh as much as 48°6 
lbs., or as little as 18-7 lbs. 
(b) In the case of complete transverse sections, from *677 to 
326, the weight per cubic foot here varying between 
42°3 lbs. and 20:4 lbs. The limits of variation in the 
determination of pressure in lbs. per square inch were 
found to be 10,049 and 3051. 
Under these circumstances averages can be of little value, but 
Prof. Schwappach indicates an approximate average sp. gr. for 
whole stems of mature trees of ‘500, and a pressure-resistance of 
about 7000 lbs. per square inch. 
Comparing recent American work in timber physics, Prof. 
Schwappach comes to the conclusion that, in regard to pressure- 
resistance, good Scotch fir timber is equal to much of the so-called 
Pitch Pine of commerce. This is more particularly the case 
where the pitch pine is derived from P. taeda, Linn., and P. mitis, 
Mich., though Scotch fir does not come up to the strength of the 
timber of P. cubensis, Gries., or P. australis, Mich.} 
Il, Witu THE SPRUCE. 
In the case of this tree the heaviest wood was found to lie 
somewhat higher up (5 metres) than in the case of the Scotch fir. 
Except at that region of the stem the sp. gr. varies but little. 
The 60 stems investigated showed no constant relationship between 
the age of the tree and the sp. gr. of the timber. Some, in fact 
the majority, produced the lightest timber in youth, and showed 
a gradually improved quality as a higher age is reached; others 
showed lighter timber between the ages of 40 and 50 years than 
1Jn the Allgemeine Forst und Jagd-Zeitung for November 1898, 
Mr B. C. Fernow maintains that Prof. Schwappach is claiming more for 
Prussian Scotch Fir than it deserves, and argues that the Prussian and 
' American methods of sampling give results unfavourable to the American 
timbers, In the December issue Prof. Schwappach adheres to his original 
contention, An International Commission, under the joint presidency of 
Prof. Wijkander, of Gothenburg, and Prof. Schwappach, will, in 1899, deal 
with the whole subject of Timber Investigation. 
