126 - On the inverted Action 
ment, as I conclude, from the leaves by an inverted actiort 
ef the alburnous vessels, . The tubers, however, by no 
-means attained their natural size, partly owing to the de- 
clining health of the plant, and partly to the stagnation of 
a portion of the true sap above the decorticated space. 
The fluid contained in the leaf has not, however, been 
proved, in any of the preceding experiments, to pass. down= 
wards through the decorticated space, and to be subsequenily 
discharged into the bark below it; but I have proved with 
amputated branches of different spacies of trees that the 
water which their leaves absorb, when immersed in that 
fluid, will be carried downwards by the alburnum, and con- 
veyed into a portion of bark below the decorticated space } 
and that the insulated bark will be preserved alive and moist 
during several days*; and if the raoisture absorbed by a leaf 
can be 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 pro- 
bably answers very important purposes in hot climates, where 
the dews are abundant and the soil very dry; for the mois- 
ture the dews afford may thus be conveyed to thé extremities 
of the roots: and Hales has proyed that the leaves absorl 
most when placed in humid air; and that the sap descends, 
either through the bark or alburnum, during the night. 
lf the inverted action of the alburnous vessels in the de- 
corticated 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 geuerated 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 lifes 
and occasions some degree of growth to take place. But a 
small portion of that fluid will be carried upwards by capil- 
ary attraction, between the bark and the alburnum, exclu 
* This experiment does no! succeed till the leaf has attained its full growth 
and maturity, aod the alburnum ofthe ennual shoot its perfect organization. 
SIE 
