NATURAL 
Conceiving, however, that a'small 
part only of the true sap would be 
expended in the production of blos- 
soms and seeds, I was anxious to 
discover what use nature would 
make of that which remained, and 
I therefore took effectual means to 
prevent the formation of tubers on 
any part of the plants, except the 
extremities of the lateral branches, 
. those being the points most distant 
from the earth, in which the tubers 
are naturally deposited. After an 
effective struggle of a few weeks, the 
plants became perfectly obedient to 
my wishes, and formed their tubers 
. precisely in the places I had assigned 
them. Many of the joints of the 
plants, during the experiment, be- 
came enlarged and turgid, and I am 
much inclined to believe, that if I 
had totally prevented the formation 
of regular tubers, these joints would 
have acquired an organization capa- 
ble of retaining life, and of affording 
plants in the succeeding spring. 
T had another variety of the potatoe 
which grew with great luxurianee, 
and afforded many lateral branches ; 
and just at that period, when I had 
ascertained the first commencing 
formation of the tubers, beneath the 
soil, I nearly detached many of these 
lateral branches from thé principal 
stems, letting them remain suspended 
by such ‘a portion only of alburnous 
and cortical fibres and vessels, as 
were sufficient 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, 
-imstead of returning down the prin- 
cipal stem into the ground, it re- 
HISTORY. 938 
mained, and formed small tubers at 
the base of the leaves of the de- 
pending branches. 
The preceding facts are, I think, 
sufficient to prove that the fluid, 
from which the tuberous root of 
the potatoe, when growing beneath 
the soil, derives its component mat- 
ter, exists previously either in the 
stems or leaves; and that it subse. 
quently 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 extend 
into the runners, which carry nutri- 
ment to the tuber, and in other in- 
stances evidently convey the true 
sap downwards, there appears little 
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 inter- 
rupted, I removed a portion of bark 
of the width of five lines, and extend. 
ing round the stems of several 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 
Biber continued to grow, deriving 
their nutriment, as I conclude, from 
the leaves by an inverted action of 
the alburnous vessels. The tubers, 
however, by no means attained their 
natural size, partly owing to the 
declining health of the plant, and 
partly to the stagnation of a portion 
of the true sap above the decorti-~ 
cated space. 
The fluid contained in the leaf has 
not, however, been proved, in any of 
the preceding experiments, to pass 
downwards through the decorticated 
space, and to be subsequently dis- 
304 charged 
