446 On the upright Growth of Vegetables. [JuNE, 
not otherwise obtain the perpendicular direction. Even were ex- 
ternal violent force applied, the effect would be the same. If we 
straighten an iron hoop, or uncoila cable, the inner or shortest side 
must elongate more than the outer side, by the difference of the 
measure of their respective curves; and in like manner when a tree 
bends to the continued action of the wind, the upper, and not the 
under side, is elongated. The elongation, therefore, will result 
from any cause which, pushing upwards, shall most stretch the 
teguments of that side by which it is most retarded; and if so, it 
cannot be admitted as an evidence that it itself is the cause why the 
germen grows upwards. 
Admitting, however, for the present, that an accumulation of sap 
takes place, and that there is a consequent elongation of the under 
side, still the principles of this hypothesis would by no means pro- 
duce perpendicularity. 
Mr. Knight seems to have assumed that as soon as the point is 
brought round to the perpendicular, the object being attained, the 
elongation will stop. But what ground is there for this supposition? 
Must not the elongation continue as Jong as the sap predominates in 
the under side? ‘The turning upof the point does not affect this 
preponderance, which must still remain on the under side, for as yet 
nothing has been added to the opposite scale. The elongation of 
the fibres must still proceed, and the curvature produced by it con- 
tinually increase; so that before the quantity of sap on both sides 
shall be equal, the point must have doubled back, and crossed the 
central line of the stem. But it would not stop even here—the 
equilibrium must be destroyed before the direction can be changed ; 
it must, therefore, still continue to deflect, till it produce the same 
effects, and by reiterated and alternate elongations every plant 
would exhibit an appearance of contortions which, it is believed, no 
one plant has ever exhibited. . 
The small alternated deflection from the perpendicular, which, 
in many trees, is produced by the thickening of the wood at the 
alternate buds, cannot be mistaken for that waving line, which is 
here supposed to be a necessary consequence of the truth of Mr. 
Knight’s hypothesis. An apt exhibition of this supposed appearance, 
and a strong evidence in favour of the accuracy of the inferences 
now drawn from these principles, is afforded by the beautiful expe~ 
yiment already quoted. 
It will be recollected that the point to which the germens of the 
beans affected by the rotatory motion all tended, was the centre of 
the wheel; but they continued their growth in the same direction 
for some time after they had passed that point. Returning to the 
centre, they must, from the same influence, have again crossed it, 
and, after a short progress, again retraced their steps in the original 
direction. ‘The stems of these beans, therefore, had they grown to 
any considerable length, must have been twisted backwards and 
forwards, the centre of the wheel forming the centre of the twists. 
‘The-tendency of a germen to point upwards in consequence of 
a 
