STATE OF THE SAP itf WINTER. 0,35 



ferent trees, to be 1.004 when extracted clofe to the ground, 

 and 1.008 at the height of feven feet. The fap cf the birch 

 was fomewhat lighter; but the increafe of its fpecific gravity, 

 at greater elevation, was comparatively the fame. When ex- 

 tracted near the ground the fap of both kinds was almoft free 

 from tafte; but when obtained at a greater height, it was 

 fenfibly fweet. The (hortnefs of the trunks of the fycamore 

 trees, which were the fubjecls of my experiments, did not 

 permit me|o extract the fap at a greater elevation than feven 

 feet, except in one inftance, and in that, at twelve feet from 

 the ground, I obtained a very fw r eet fluid, whofe fpecific gra- 

 vity was 1.012. 



I conceived it probable, that if the fap in the preceding cafes The fap firft 

 derived any confiderable portion of its increafed fpecific gra- Jj™J!5^ S jJ en '* 

 vity from maltsr previoufly exifting in the alburnum, I fliould ftiews that its 



find fome diminution of its weight, when it had continued to augmentation 



. riiL • wa s had from 



flow tome days from the fame incifion, becaule the alburnum in matter in the 



the vicinity of that incifion would, under fuch circumflances, a!bumum * 



have become in fome degree exhaufted: and on comparing 



the fpecific gravity of the fap which had flowed from a recent 



and an old incifion, I found that from the old to be reduced to 



1.002, and that from the recent one to remain 1.004, as in the 



preceding cafes, the incifion being made clofe to the ground. 



Wherever extracted, whether clofe to the ground, or at fome 



diftance from it, the fap always appeared to contain a large 



portion of air. 



In the experiments to difcover the variation in the fpecific Tt is difficult t» 



gravity of the alburnum of trees at different feafons, fome f ex P e £- 



*» J v * ments on the 



obflacles to the attainment of any very accurate refults pre- denfity or fp. 

 tented themfelves. The wood of different trees of the fame g" vlt y of thc 

 fpecies, and growing in the fame foil, or that taken from 

 different patts of the fame tree, pofleffes different degrees of 

 folidity; and the weight of every part of the alburnum ap- 

 pears to increafe with its age, the external layers being the 

 lighteft. The folidity of wood varies alfo with the greater or 

 lefs rapidity of its growth. Thefe fources of error might ap- 

 parently have been avoided by cutting off, at different feafons, 

 portions of the fame trunk or branch: but the wound thus 

 made might, in fome degree, have impeded the due progrefs 

 of the fap in its afcent, and the part below might have been 

 made heavier by the ftagnation of the fap, and that above 



lighter 



