272 EXACT PROGRESSIVE MEASUREMENT OF TREES. 



forty years its wood has grown at a pace scarcely less than in 

 a much lower altitude and finer climate ; but that between its 

 fortieth and sixtieth year this rate ceases, and not gradually, 

 but rather suddenly. In three or four years the width of the 

 annual layers of wood is reduced to one-half or a third of what 

 it was. The reduction goes on increasing, and at last the rings 

 are so narrow that they can scarcely be counted. I can see 

 no explanation of these curious facts so reasonable as that, the 

 scanty soil being exhausted of those saline matters, which are in 

 part essential for the formation of leaves and wood, growth must 

 become less vigorous, and even cease, long before the natural 

 limit in more favourable circumstances. The question then will 

 be, what saline matter is lost by the soil and appropriated by 

 the trees, and what sort of manure will replace the loss ? 



But foresters must be taught to observe minutely, and to record 

 with accuracy. For this purpose I reproduce the recommenda- 

 tions recently adopted by the Meteorological Society of Scotland. 



The observer should note : — 



1. The elevation of the site above sea-level. 



2. Whether it is on a hill slope, steep or gentle, or on a terrace on the 

 slope, or on a level plain, or in a narrow gorge. 



3. If on a hill slope, the direction of its face by compass, and whether 

 there is protection from direct winds by heights above or around. 



4. Anything peculiar in the meteorology of the district, and differing 

 from that of the adjacent country. 



5. The nature of the soil, its depth, and the nature of the subsoil. 



6. Whether the wood has been subjected to timely and judicious thinning 

 or pruning. 



7. Whether it has undergone any nutritive or stimulating treatment. 



8. Twenty trees should be chosen growing near one another, and not at 

 the very verge of the wood. 



9. All ill-thriving trees should be rejected, and had better be felled, but 

 otherwise selection is not advisable. 



10. Scotch fir, larch, spruce, and oak will probably be the standard 

 subjects of observation, but any other species maybe usefully observed also. 



11. Any change of treatment during the period of observation, or any 

 injury from storms, insects, &c. 



12. Trees whose bark is apt to scale off are obviously unsuitable. In 

 others the bark is apt to crack and start up, in which case the elevation 

 should be levelled with the knife or rasp. 



13. The measurement should be made usually about five feet from the 

 roots. But, in more general terms, the place of measurement should avoid 

 the swelling at the base, and that under the spring of the chief branches. 



14. All lumps should be avoided, and little excrescences in the line of 

 measurement should be levelled w^ith the knife or rasp, if this can be done 

 without injury to the tree. 



15. The tape should be applied as level as possible if the trunk be erect, 

 but at right angles to the line of the trunk if it be a little inclined. Trees 

 much inclined may be excluded. 



16. The tape should be long enough to go round the whole trunk. It 

 should be of a material that does not easily lengthen by stretching. The 



