RECENT INVESTIGATIONS IN REGARD TO QUALITY OF TIMBER. 287 
either before or after that period ; while in others the best timber 
of all was produced in early life, and a gradually deteriorating 
quality in the later stages. In this connection the determinating 
factor would appear to be the system adopted in regenerating or 
establishing the forest. If the forest has originated by planting 
on a clear-felled area, the young trees will show very rapid 
growth at an early stage, and such timber will be of low sp. gr. 
If, on the other hand, the wood has been renewed by natural 
seeding under a shelter-wood, the young trees will have made but 
slow growth in youth, and the timber will be heavy. 
The spruce exhibits a much greater tendency to vary, both as 
regards sp. gr. and pressure-resistance, than the Scotch fir, Trees 
from the same forest frequently give most contradictory results, 
a fact that had previously been emphasised by R. Hartig. The 
sp. gr. of spruce timber from a first-class situation may be as high 
as that of good Scotch fir, though in the case of timber from poor 
soils there is a marked difference in the two trees in regard to 
this physical property. It is thus unsafe to attempt to generalise 
from investigations on a few stems, a very large amount of work 
being necessary to furnish a reliable average. 
Shrinkage is most marked at a height of 4 metres (14 7%), and 
gradually, though slowly, decreases towards the crown, where it 
amounts to 11-12 7. 
Where the wood of sections from mature trees was examined, 
it was found that the central wood shrank least, and the outer 
wood most, though the difference is not more than 2 7%, and gener- 
ally even less. Resistance to pressure is at a maximum where 
the sp. gr. is highest ; in fact, the general relationships between 
these two properties, that have already been indicated as holding 
good for the Scotch fir, have also been established for the spruce. 
The limits of variation of sp. gr. in the case of definite periods 
of growth were found to be 621 and ‘261; while, in the case of 
complete sections, the variations were ‘563 and ‘371. Prof. 
Schwappach gives ‘460 as the average sp. gr. for the whole 
timber of a spruce tree 100-120 years old (-500 for the Scotch 
fir); and an average pressure-resistance of 6500 lbs, per square 
inch (about 7000 lbs. for the Scotch fir), the limits being 8772 
and 4657, 
Tit. Wirn tue Sitver Fir, 
The twelve trees of this species submitted to investigation 
were all taken from two forests in Thiiringia that had yielded 
