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T816.] On the upright Growth of Vegetables. 443 
the elongation of the lower side, cannot be supposed to have more 
influence in arresting its progress when arrived at perpendicularity, 
than the centripetal force to arrest the progress of the bean when its 
germen had reached the centre of the wheel ; certainly its influence 
could not be so powerful; for by the hypothesis in question there is 
no principle which gives the germen a tendency to perpendicularity, 
that feature of its growth being stated to be the effect of the elon- 
gation. The point of the germen, therefore, would have no 
antagonist to contend with, in continuing its curvature past the 
centre of the stem. It would meet with no opposition till an accu- 
mulation of sap on the under side should operate so powerfully as to 
change its direction ; and we must infer that the contortions pro- 
duced by the alternate elongations would be much greater than 
those exhibited in the experiment, by the stems passing and repass- 
ing the centre of the wheel. 
The hypothesis stands also contradicted by the facts we constantly 
observe in the progress of straightening young plants and shoots of 
trees. The elm, the beech, and some other trees, evolve at once 
almost the whole annual shoot. ‘These shoots are then very tender, 
and of course pendulous. They straighten themselves, however, 
considerably during the first season, and generally, when well 
sheltered, approach near to the perpendicular in the course of the 
next. On the principles of Mr. Knight’s hypothesis the process of 
straightening ought to commence at the top, where the point is 
turned up; yet every day’s experience proves that they gain their 
perpendicularity by a general progressive change on the whole twig, 
By the elongation of the under side there is only provision made for 
tnrning up the point. No principle is furnished likely to operate in 
favour of the deflected stem. Indeed, the elongation of one side 
more than the other, instead of aiding a plant already curved to | 
regain the perpendicular, seems better calculated to perpetuate the 
curvature. 
But it may be questioned if there be in reality any such accumu- 
lation of sap, any such unvaried elongation of the under side of all 
deflected germens, It is obvious tbat, if it acts at all, it must act 
always, whatever twistings or contortions the continued elongation 
of one side only might produce. If the cause exists, it is situated 
beyond the reach of those sinister accidents which would affect or 
counteract a principle of external agency. Unless, therefore, we 
can recognise its influence in every case, we may,conclude that we 
have still to discover the legitimate principle. 
In young shoots the sap abounds in every part. We find, accord- 
ingly, that if a germen be prevented by any overpowering force 
from altering its position, it will grow, though confined to a hori- 
zontal direction, and both sides will elongate equally. It sometimes 
happens with the bean, and always with the onion, that the point 
of the germen remains long confined within the lobes of cotyledon 
after the germen itself has attained considerable length. From this 
circumstance it is bent into a semicircle, both ends being immersed 
6, 
