258 Anatomical Description of the Fir Tree. 



tough membranes. The radiates frequently cross these larger 

 vessels ; and the genera] appearance of the blood in them both, 

 where they pass each other, seems to indicate, that tlicy com- 

 municate together in their passage. The longitudinal vessels 

 however appear to contain a much greater portion of air than 

 the radiates. In all the specimens that I have examined, these 

 largest longitudinal vessels are generally from one-eighth to 

 three-eighths, and sometimes half an inch apart, on the circular 

 line of the plant; and about three of them in the breadth of 

 each concentric ring, or year's growth. In other cases they 

 are much further apart, but thev are extremely irregular. Some- 

 tim.cs three, four, or five will occur in a cluster. Where there 

 is such a cluster, the turpentine will generally be found exhaling 

 from the plant bv these canals. This however is far more com- 

 mon in the silver fir, the Weymouth pine, and some others, than 

 in the pinus silvesliis, or Scotch fir. 



The chemical analysis of the woody fibre of this plant in va- 

 rious exi^eriinents has yielded such different results, that 1 think 

 it unnecessary to mention them. I shall therefore only take 

 notice of the juices, and the process of their elaboration as they 

 relate to temperature. A low temperature appears most con- 

 genial to the fir tree, although it is to be found in very warm 

 climates. Yet from the nature of its juices it cannot be expected 

 to arrive at great perfection in a lower degree of north latitude 

 than S.'jf or 5-1°; or rather except in a mean temperature that 

 is proportionate to these degrees of latitude, say 45^ or 46° of 

 Fahrenheit. It is necessary too, that the temperature should 

 approach much nearer to permanency, than is required by most 

 other plants. This is most obvious with respect to that called 

 the Scotch fir, which by the by is to be found in every country 

 in Europe ; is the species that furnishes the red or yellow deal ; 

 and is confessedly of the best grain and texture, and most dura- 

 ble of any sort of fir vet known, the larch excepted. 



The svcctis propriiis of fir trees is of a peculiar kind, and 

 known by the general name of turpentine, different varieties of 

 which are produced bydiflerent species of the fir. It is obtained 

 in considerable quantity by boring holes, or c>itting deep notches, 

 in the trunk of the tree ; but more expeditiously by means of 

 artificial heat, when it assumes the name of tar To procure 

 this, the wood of the trunk, branches, and roots, is heaped to- 

 gether, covered with turf, and then set on fire, so as to be ex- 

 posed to a smothering combustion, as in preparing charcoal. A 

 gutter is formed at the bottom, to receive the turpentine, which 

 flows out strongly impregnated with carbon^ whence the tar ac- 

 quires its black colour. 



Ill 



