of the allurnous Vessels of Trees. 125 
experiment became enlarged and turgid; and [ am much 
inclined to believe, that if [ had totally prevented the forma- 
tion of regular tubers, these joints would have acquired an 
organization capable of retaining life, and of affording tee 
in the succeeding spring. 
T had ee oe variety of the potatoe, “which erew with 
great Juxuriance, and afforded many lateral branches; and 
just at that period, when I had ascertained the first com- 
mencing formation of the tubers beneath the soil, I nearly 
detached many of these lateral branches from the principal 
stems, letting them remain suspended by such a portion 
only of alburnous and cortical fibres and vessels as were suf- 
ficient to preserve life. In this position I conceived, that if 
their leaves and stems contained any unemployed true sap, 
it could not readily find its way to the tuberous roots, its 
passage being obstructed by the rupture of the vessels, and 
by gravitation ; and I had soon the pleasure to see, that, in- 
stead of returning down the principal stem into the ground, 
it remained and formed small tubers at the base of the leaves 
of the depending branches. 
The preceding facts are, T think, sufficient to prove that 
the fluid, from which the tuberous root of the potatoe, when 
growing bencath the soil, derives its component matter, 
exists previously either in the stems or leaves; and that it 
subsequently descends into the earth; and as the cortical 
vessels, during every period of the growth of the tuber, are 
filled with the true sap of the plant, and as these vessels ex- 
tend into the runners, which carry nutriment to the tuber, 
and in other instances evidently convey the true sap down- 
wards, there appears litle reason to doubt that through these 
vessels the tuber is naturally fed. 
To ascertain, therefore, whether the tubers would continue 
to be fed when the passage of the true sap down the cortical 
vessels was interrupted, I removed a portion of bark of the 
width of five lines, and extending round the stems of se- 
veral plants of the potatoe, close to the surface of the ground, 
soon after that period when the tubers were first formed. 
The plants continued some time in health, and during that 
period the tubers continued to grow, deriving their nutri- 
ment, 
