Anatomical Description of Ihs Fir Tree. 20 1 



fibres appears in every way the same as tlte otliers, and their 

 number the same and no more than that of the other parts of tlie 

 wood in an cqnal space ; so that the vvh-jle number oi the woody 

 fibres of the fir, like those of othe; trees, may be presumed to be 

 formed in what is commonly termed the vegetating season of 

 the year: but a fev/ near the outside are rendered more hard 

 and firm, by the change of temperature acting upon them when 

 tire heat is not sufficiently strong to penetrate deep into the body 

 of the wood ; for from the nature of the juice a blink of .sun- 

 shine even in the time of frost and snow will most probably af- 

 fect the turpentine, as it aifects the motion of the sap of other 

 trees in a warmer season. The heat however having little force, 

 and the time being probably short before it is abstracted again by 

 the ambient air, which gives it the countermorion, it cainiot pe- 

 netrate deep into the wood. 



'If Gay-Lussacand Thenard be correct in their opinion, " tliat 

 a vegetable substance is always resinous, or oily, or spirituous, 

 whenever it contains oxvgen in a smaller proportion to the hy- 

 drogen, than it exists in water ; and that a vegetable substance 

 is always acid, whenever the oxygen it c-ontaius is to the hydro- 

 gen in a greater proportion than in water;" it is at least pro- 

 bable, that the turpentine part of the juice is principally formed 

 in the winter, or at other seasons of low temperature, when the 

 hydrogen may more readily be obtained for the necessary olie^- 

 mical union than in a high temperature ; and the acid may for 

 the same reason be principally formed ia a higher temperature, 

 when the chemical union with oxygen is more readily effected. 



Whether the causes of the respective chemical combinations 

 be sutficLently well understood, or not, thus far appears tpiite 

 clear, that the dark part of the concentric ring:= principally as- 

 sumes its colour in the winter season ; and is more strongly di- 

 stinguished from the other part of the ring in trees that grow in 

 warm situations, or in the skirts of a wood, than in those in the 

 interior of a wood, where tlic temperature is moie permanent. 

 Not that there is much difference in the quantity of turpentine 

 in the whole ring ; for, if the dark part have more turpentine 

 than its due proportion, the other part has less. 



It is probable too, that the high temperature of our summers, 

 or vegetating seasons, prevents that chemical union, which con^ 

 stitutes the turpentine, or juice of the fir tree: and further, that 

 which is afterward formed in the winter is partly driven off, as 

 ftlready mentioned, in the following summer. 



The fir known by the name of the pitch pine of America, so 

 much used in this country of late, which grows in a cold climate 

 \n low or wet land, has very little resiji, but a very large pro- 



H portion 



