Mr. Knight on the Origin and Formation of Roots, ijg 
arrived at the top of the cutting through the alburnum would 
be there employed, as I had observed in many similar cases, 
in generating buds, and that these buds would be protruded 
where the bark was young and thin, and consequently afforded 
little resistance.* I had also proved the bark to be better 
calculated to carry the sap towards the roots than in the op- 
posite direction, and I thence inferred that as soon as any 
buds, emitted by the cuttings, afforded leaves, the sap would 
be conveyed from these to the lower extremity of the cuttings 
by the cortical vessels, and be there employed in the forma- 
tion of roots. -f- 
Both the alburnum and bark of trees evidently contain their 
true sap ; but whether the fluid which ascends in such cases 
as the preceding through the alburnum to generate buds, be 
essentially different from that which descends down the bark 
to generate roots, it is perhaps impossible to decide. As na- 
ture, however, appears in the vegetable world to operate by 
the simplest means ; and as the vegetable sap, like the ani- 
mal blood, is probably filled with particles which are endued 
with life, were I to offer a conjecture, I am much more dis- 
posed to believe that the same fluid, even by merely acquiring 
different motions, may generate different organs, than that 
two distinct fluids are employed to form the root, and the bud 
and leaf. 
When alburnum is formed in the root, that organ possesses, 
in common with the stem and branches, the power of produc- 
ing buds, and of emitting fibrous roots, and when it is de- 
tached from the tree, the buds always spring near its upper 
end, and the roots near the opposite extremity, as in the 
* Phil. Trans, for 1805. 
