of the alburnous Vessels of Trees. 301 
thus transferred, it appears extremely probable that the true 
sap will pass through the same channel. This power in the 
alburnum to carry fluids in different directions probably 
answers very important purposes in hot climates, where the 
dews are abundant and the soil very dry ; for the moisture 
the dews afford may thus be conveyed to the extremities of 
the roots : and Hales has proved that the leaves absorb most 
when placed in humid air ; and that the sap descends, either 
through the bark or alburnum, during the night. 
If the inverted action of the alburnous vessels in the decor- 
ticated space be admitted, it is not difficult to explain the 
cause why some degree of growth takes place below such 
decorticated spaces on the stems of trees ; and why a small 
portion of bark and wood is generated on the lower lip of 
the wound. A considerable portion of the descending true 
sap certainly stagnates above the wound, and of that which 
escapes into the bark below it, the greater part is probably 
carried towards, and into, the roots ; where it preserves life, 
and occasions some degree of growth to take place. But a 
small portion of that fluid will be carried upwards by capillary 
attraction, between the bark and the alburnum, exclusive of 
the immediate action of the latter substance, and the whole 
of this will stagnate on the lower lip of the wound ; where I 
conceive it generates the small portion of wood and bark, 
which Hales and Du Hamel have described. 
I should scarely have thought an account of the preceding 
experiments worth sending to you, but that many of the 
conclusions I have drawn in former memoirs appear, at first 
view, almost incompatible with the facts stated by Hales and 
