SAP OF TREES DURING WINTER. 113 



ascertained the specific gravity of both with scarcely any variation in the 

 result. But when I omitted the medulla, and parts adjacent to it, and 

 used the layers of wood which had been more recently formed, I found 

 the specific gravity of the winter-felled wood to be only 0.583, and that 

 of the summer-felled to be 0.533 ; and trying the same experiment with 

 similar pieces of wood, but taken from poles which had grown on a 

 different stool, the specific gravity of the winter-felled wood was 0.588, 

 and that of the summer-felled 0.534. 



It is evident that the whole of the preceding difference in the specific 

 gravity of the winter and summer felled wood might have arisen from a 

 greater degree of contraction in the former kind, whilst drying ; I there- 

 fore proceeded to ascertain whether any given portion of it, by weight, 

 would afford a greater quantity of extractive matter, when steeped in 

 water. Having therefore reduced to small fractions 1000 grains of each 

 kind, I poured on each portion six ounces of boiling water ; and at the 

 end of twenty-four hours, when the temperature of the water had sunk 

 to 60, I found that the winter-felled wood had communicated a much 

 deeper colour to the water in which it had been infused, and had raised 

 its specific gravity to 1.002. The specific gravity of the water in which 

 the summer-felled wood had, in the same manner, been infused was 1.001 . 

 The wood in all the preceding cases was taken from the upper parts of 

 the poles, about eight feet from the ground. 



Having observed, in the preceding experiments, that the sap of the 

 sycamore became specifically lighter when it had continued to flow during 

 several days from the same incision, I concluded that the alburnum in 

 the vicinity of such incision had been deprived of a larger portion of its 

 concrete or inspissated sap than in other parts of the same tree : and I 

 therefore suspected that I should find similar effects to have been pro- 

 duced by the young annual shoots and leaves ; and that any Driven weight 

 of the alburnum in their vicinity would be found to contain less extractive 

 matter than an equal portion taken from the lower parts of the same 

 pole, where no annual shoots or leaves had been produced. 



No information could in this case be derived from the difference in the 

 specific gravity of the wood ; because the substance of every tree is most 

 dense and solid in the lower parts of its trunk : and I could on this account 

 judge only from the quantity of extractive matter which equal portions of 

 the two kinds of wood would afford. Having therefore reduced to pieces 

 several equal portions of wood taken from different parts of the same 

 poles, which had been felled in May, I poured on each portion an equal 

 quantity of boiling water, which I suffered to remain twenty hours, as in 



