fbe SAP in TREES, 5 



" quantity ; its progrefs is always rapid ; it fpeedily reaches the 

 " tops of the branches, from whence it quickly pafles again to- 

 " wards the roots *." 



BUT after the doctrine of the circulation of the fap has been 

 agitated for above a century paft ; after fo many obfervations, 

 and fuch lengthened philofophical difcuffions upon the fubjecl: ; 

 is it not furprifmg that this enquiry, firft darted by Dr LISTER, 

 and fince fuggefled by Dr HALES, mould have been fo much 

 overlooked, and mould ftill remain undetermined by experiment, 

 when it is evidently the previous and leading enquiry on the 

 fubjea ? 



M. BONNET, indeed, in the above paffage, feems to think, 

 that the decifion of this queflion by experiment mufl be ex- 

 tremely difficult, if not impracticable. But that this is far from 

 being the cafe, will appear from the fequel of the prefent paper. 



THE principal experiment here recorded was therefore made, 

 in order to know whether all the parts of a tree bleed at once, 

 or by fucceffion : How far the afcent and diffufion of the fap 

 depends on the temperature of the air : To trace the route which 

 it obferves, and to obtain fatisfaction concerning what is called 

 its recidivatioTiy and in feveral other particulars relative to its 

 movement. 



FROM this experiment alfo, fome light was expelled concern- 

 ing a noted problem in vegetation, Why the terminating buds 

 of trees are the firft which are difclofed in the fpring. 



THE tree on which this experiment was made, was a vigorous 

 young birch, thirty feet high, and its ftem twenty-fix inches in 

 circumference at the ground. 



ON the i ft of February, there was a hole bored in the trunk 

 of this tree, clofe by the ground, and one of its branches 

 cut at the extremity, in order to difcover when and where the 

 running of the fap would firft appear. This was repeated every 



fecond 



* BONNET fur 1'Ufage des Fcuilles, p. 284. 



