284 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
autumn wood increases the sp. gr., and, concurrently, the quality 
of the timber.” 
The latitude has considerable influence on the sp. gr. of timber, 
and, in the case of the Scotch fir, it may be said that heavier 
timber is produced in the north of Germany than in the south. 
This is in agreement with the accepted views of British foresters 
on the subject, who are well aware that Baltic pine is of higher 
quality than pine grown in, say, the south of England. As 
Hartig has pointed out, the rapid transition from winter to 
summer, that is characteristic of high latitudes, is unfavourable 
to the development of spring wood, so that, in timber from such 
regions, the autumn wood is relatively very abundant. 
If Scotch fir timber grown in any particular district, but on 
different classes of soil, be examined, it will be found that the 
better the soil the heavier the timber. This presupposes, of 
course, that the forests in each case are of normal density, or 
otherwise the trees grown on the good soil would show so much 
more rapid growth that this factor might upset the influence of 
the quality of the situation per se. The worst timber of all was 
found to be that grown on peat. 
As regards shrinkage, it was found that the wood of young 
trees shrinks more than that formed by old trees. Thus the 
average shrinkage of the timber of a 30-year old pine is about 
15°7 %, whereas the wood formed between the 30th and 60th 
years of a 60-year old tree shrinks only to the extent of 
11:1 % Where, however, the degree of shrinkage of the wood 
in a complete section of a 60-year old tree is investigated, it is 
found that the wood of the inner 30 rings shrinks appreciably 
less than the wood of the outer 30 rings, a fact that is doubt- 
less due to the formation of duramen in the centre of the tree. 
But for this, the inner wood of trees grown on good soil would 
shrink more than the outer. The variations in shrinkage in 
wood produced at different periods from 30 to 150 years are 
very small. 
Resistance to crushing is influenced by factors similar to those 
that affect the sp. gr., though not always in the same way or to 
the same extent. Timber taken from near the base of a tree is 
usually more resistant to a vertical load than specimens taken 
higher up the stem, the power of resistance diminishing rapidly 
up to the height of 5 metres (about 164 feet), and much more 
slowly afterwards; in fact, in a stem 25 metres long, it may be 
