• Variation of Water in Trees. lOY 



HYDRATION OF WOOD FROM LIVING TREES. 



The specimens, upon which the principal facts of this paper 

 are based, were collected as sections of living trees, repre- 

 senting on the one hand, branches of two years growth, and 

 on the other, branches from two to four years old. For the 

 obvious reason that the bark could not be properly separated 

 from the wood with any degree of uniformity, it was left on in 

 every case, so that in all the determinations here given, the 

 results show the combined percentage of water in wood and 

 bark. Obviously, this gives a result which differs materially 

 from that which would be obtained if bark and wood were 

 considered separately. Also, while care was taken not to col- 

 lect specimens in which the dead bark was strongly develop- 

 ed, thus securing as great uniformity as possible, the very 

 fact that the bark was present, as well as the certainty of its 

 being variable in structural character and thus also in hydra- 

 tion, as collected even from the same species at different sea- 

 sons, rendered variations in the results unavoidable. This 

 will doubtless appear upon examining individual cases, but 

 the error from this source is reduced in the aggre- 

 gate, so that the mean results, in view of all the precautions 

 taken, may doubtless be accepted as correct. 



From an examination of the results that follow, it will 

 appear that, comparing the younger with the older wood, the 

 percentage of water is sometimes greater in one, sometimes 

 greater in the other, apparently conforming to structural 

 peculiarities of the species. The mean results, however, 

 show clearly what we might infer upon theoretical grounds, 

 viz., that in the youngest growth, as also in the sap wood, 

 the percentage of water is higher by two per cent, than in 

 the older growth where the heart-wood is in relative excess. 

 This is found to hold true in the mean results, not only for 

 each season, but also for all seasons ; in the former case, 

 however, this difference shows a variation of from 0.8 per 

 cent, to 3.3 per cent, of water. 



