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IV. EXPERIMENTS AND OBSERVATIONS ON THE MOTION OF THE SAP 



IN TREES. 



[Read before the ROYAL SOCIETY, February 16, 1804.] 



IN the Observations on the Descent of the Sap in Trees, which I last 

 year took the liberty to lay before the Royal Society, I offered a con- 

 jecture, that the vessels of the bark, which pass from the leaves to the 

 extremities of the roots, were, in their organization, better calculated to 

 carry the fluids they contain towards the roots than in the opposite 

 direction. I had not, however, at that time, any experiment directly to 

 support this supposition ; but I thought the forms generally assumed by 

 trees in their growth, evinced the compound and contending actions of 

 gravitation, and of an intrinsic power in the vessels of the bark, to give 

 motion to the fluid passing through them. In the account of the experi- 

 ments which I have now the honour to address to you, I trust I shall be 

 able to adduce some interesting facts in support of that inference. 



Having selected, in the spring of 1802, four strong shoots of the vine, 

 growing along the horizontal trellis of my vinery, I depressed a part of 

 each shoot, whilst it was soft and succulent, about three inches deep, 

 into the mould of a pot placed beneath it for that purpose ; but without 

 making any wound, or incision, in the young shoots thus employed as 

 layers. 



In this position they remained during the succeeding summer ; and, in 

 the autumn, had nearly filled the pots, which were ten inches in dia- 

 meter, with their roots. As soon as the leaves had fallen, the layers 

 were disengaged from the parent stocks ; and about five inches of wood, 

 containing one bud, were left, both at the proper and the inverted end 

 of each layer. Every bud was also, by previous management, made to 

 stand at an equal distance from the mould in the pots, and with an equal 

 elevation, of about thirty-six degrees. About one inch of wood was 

 likewise left at each end of every layer, beyond the buds. 



In the succeeding spring, the buds vegetated strongly, both at the 

 proper and at the inverted ends of the layers, as the experiments of 

 Hales and Duhamel had given me reason to expect ; and in one 

 instance, the bud at the inverted end of the layer grew with greater 

 vigour than that at its proper end : but the growth of these buds was 

 not the object which I had in view, 



I have already stated, that nearly an inch of wood was left at each 

 end of every layer, beyond the bud ; and to this wood, at the inverted 

 ends of the layers, my attention was chiefly directed : for if the vessels 



