SECT. III. CIRCULATION OF JUICES. 243 



matter supposed to be deposited in the alburnum is 

 the true cause of the wood's superior quality, then 

 the circulation cannot take place ; because on the 

 supposition in question the matter that is thus de- 

 posited ought not to be again abstracted. Indeed 

 it seems to be doubtful whether the hypothesis is 

 good in any of its parts ; for as on the one hand the 

 circulation rests on no admissible proof, so on the 

 other the superior quality of the winter felled wood 

 is well enough accounted for by its becoming more 

 condensed. 



It is no proof of the circulation of the vegetable 

 fluids to say that the proper juice may even be seen 

 in the alburnum of some plants, as in the example 

 of the Fig. For since the alburnum is itself ori- 

 ginally formed of the proper juice, it cannot during 

 the first year be otherwise than mixed with it ; and 

 if it should occasionally be found even in the 

 matured wood, it may be nothing more than the 

 portion that was originally deposited, now in an 

 inspissated state. Nor is the induration of the 

 wood to be regarded as proceeding from the intro- 

 susception of some additional substance into the 

 alburnum, rather than from its condensation, owing 

 to the mere change of colour which takes place in 

 that process from a white to a dark brown ; or to its 

 increased durability, as supposed by Mr. Knight,* 

 because the effects in question may be easily ac- 

 counted for, even upon the principle of condensa- 

 *Phil. Tran. 1806, 

 R 2 



