23-fc STATE OF THE SAP ftf WlNTEK. 



wood feem more juftly to warrant the conclufion, that fome 



—but probably fubftance has been added to, inftead of taken from it, and 

 to its prefence. . -, ... „ ^ . 



many circumftances induced me to fufped that this iubftance 



is generated, and depofiled within it, in the preceding fummer 



and autumn. 



Full grown Du Hamel has remarked, and is evidently puzzled with the 



»oft S p P lent l ifu < lly c ' rc umftance, that trees perfpire more in the month of Auguft, 



when the leaves are full grown, and when the annual (hoots 



have ceafed to elongate, than at any earlier period; and we 



cannot fuppofe the powers of vegetation to be thu' actively 



employed, but in the execution of fome very important opera- 



— and at this tion. Bulbous and tuberous roots are almoft wholly generated 



{relative poVers a ^ !er ^ e leaves and (terns of the plants, to which they belong, 



appear to be em- have attained their full growth; and I have* conitantly found, 



c'eafin '"the" * n m ^' P ra ^ ce as a former, that the produce of my meadows has 



growth of the been immenfely increafed when the herbage of the preceding 



vegetable. y ear j )at | remained to perform its proper office till the end of 



the autumn, on ground which had been mowed early in the 



fummer.' Whence I have been led to imagine, that the leaves, 



" both of trees and herbaceous plants, are alike employed, during 



the latter part of the fummer, in the preparation of matter 



calculated to afford food to the expanding buds and bloiToms 



of the fucceeding fpring, and to enter into the compofition of 



new organs of ailimilation. 



If this be the If the preceding hypothecs be well founded, we may expeel 



hffounfthlt t0 find that fome cna,1 g e wil1 gradually take place in the 

 the aqueous fap qualities of the aqueous fap of trees during its afcent in the 



mutt beakered fpring: and that any given portion of winter-felled wood will 



in its afcent; r °' . J r , r r 



and the winter at lne lanie time poflefs a greater degree or fpecinc gravity, 



feiled wood will anf J yidd a larger quantity of extractive matter, than the fame 



quantity of wood which has been felled in the fpring or in the 



early part of the fummer. To afcertain thefe points I made 



the experiments, an account of which I have now the honour 



to lay before you. 



Experiments. As early in the laft fpring as the fap had rifen in the fyca- 



Bhch and fyca- more d bj t j d | pc ifipns into the trunks of thofe 

 more in fpring f 



gave fap moft trees, fome clofe to the ground, and others at the elevation of 

 aqueous near the f even f ee ^ anf j I readily obtained from each incifion as much 

 denfer and more fa p as I wanted. Afcertaining the fpecific gravity of the fap 

 jaccharine the p f each tree, obtained at the different elevations, I found that 

 g er up. ^ ^ c ^ ^ ^ fycamore with very little variation, in dif- 

 ferent 



