282 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
immediately underneath and within the crown. The average 
figures for 33 trees over 90 years old are here given, 
Height on stem. Average sp, gr. 
1 metre ‘O17 
4S. cds ‘519 
eo) ene ‘466 
DD es 3g “445 
16a. 435 
yt 439 
24, 444 
These figures show that the sp. gr. falls rapidly up the height of 
8 metres, and that the decrease is much less marked between 
this point and 16 metres. Higher up than this there is a slight 
recovery. 
The sp. gr., in the case of timber grown on the better classes 
of soil, is at its maximum between the 30th and 60th rings, 
probably culminating about the 60th year. 
Thus, in the case of 64 trees from Brandenburg :— 
| 
Limits of Age of - | Sp. Gr. of the Wood between the Rings. 
Tree, in Years. | 
| 0-30 | 31-60 | 61-90 | 91-120 |121-150 151-180\181-210 
31- 60 “454 486 The A uO ah Tex: 25 
61- 90 “490 490 “E80 es 
91-120 *475 "498 a7 | “AOE | ace 
121-150 515 | °520 “504 "484 464 ik ied 
|. Over 150 489 | °524 “544 512 471 “441 427 
| | 
The effect of the improved sp. gr., under the influence of 
formation of duramen, is well seen in the column which refers 
to the wood of the 31st to the 60th rings, both inclusive. In the 
case of a tree 31-60 years old, there could, of course, be but little, 
if any, duramen in these rings, and the sp. gr. is a low one, 
namely, 486. With trees up to 90 years of age there would be 
more pronounced formation of duramen in the 30 rings in ques- 
tion, and now the sp. gr. is ‘490. In the case of still older trees 
(91-120 years), the duramen would be well formed in the 31st to 
60th rings, so that the sp, gr. is now ‘498, and rises in older trees 
to ‘520 and ‘524. 
The condition of things is distinctly different in the case of trees 
grown on the poorer classes of soil. Here the heaviest wood igs 
