^0 inn. knight's EXPEniMJiN-fA., 



lower ends of some cattings of the Applotretf 

 and Horse-chesnut into an infusion of the skina 

 ot a very black grape in water, an excellent 

 liquor for tiie purpose. Tlie result was simi- 

 lar. But Mr. Knight pursued his observations 

 much further than Dr. Darwin had done; for 

 he traced the coloured liquid even into the 

 leaves, " but it had neither coloured the bark 

 nor the sap between it and the wood ; and the 

 medulla was not affected, or at most was very 

 slightly tinged at its edges." VJiil. Trans, 

 for 1801, p,335. 



The result of all Mr. Knight's experiments 

 and remarks s^eems to be, that the fluids des- 

 tined to nourish a plant, being absorbed by 

 the root and become sap, are carried up into 

 the leaves by these vessels, called by him cen- 

 tral vessels, from their situation near the pith. 

 A particular set of them, appropriated to each 

 leaf, branches oft^, a few inches below the leaf 

 to which they belong, from the main channels 

 that j>ass along ihe alburnum, and extend 

 from the fibres of the root to the extremity 

 of each annual shoot of the plant. As -they 

 approach the leaf to which they are destined, 

 the central vessels become move numerous, 



