1819.] Divection of the Radicle and Germen. 257 
will continue indeed to descend to a much greater depth, if not 
prematurely taken up. At this moment there lies before me the 
root of a radish sown in the month of March or April last, and 
which from being allowed to stand to come to seed, and not 
taken up till a few days ago, measures one foot in length from 
the base to the apex, with a diameter of 21 inches at the widest, 
three inches having been raised above the soil, and nine buried 
under it. Now itis evident that this growth was occasioned by 
the introsusception and deposition of particles throughout its 
whole extent. The turnip seems also to be an example in point. 
Warranted, therefore, by these facts, | contend that gravita- 
tion, finds no facility whatever in carrying down the radicle 
which it would not find also in carrying down the plumelet ; and 
that whatever may be its agency upon the one, it ought to be 
precisely the same upon the other. If the root grows down- 
wards by virtue of gravitation, so should the stem; and hence 
by force of the counteracting power in Mr. Knight’s experiment, 
both root and stem ought to have receded from the circumfe- 
rence of the wheels outwards, like a thong of leather nailed to 
it by the middle, and the machinery put in motion. Such is 
Mr. Knight’s account of the rationale of the descent of the root. 
Let us now proceed to his account of the rationale of the ascent 
of the stem. 
“ If (says Mr. Knight) the motion and consequent distribu- 
tion of the true sap be influenced by gravitation, it follows that 
when the germen, at its first emission, or subsequently, deviates 
from a perpendicular direction, the sap must accumulate on its 
under side.” * But the motion and consequent distribution of 
the true sap is proved to be very little, if at all, influenced by gra- 
vitation, from the fact of its easy ascent in the pendant shoot of 
the weeping willow, and in other pendant shoots—a fact that 
Mr. Knight will not refuse to acknowledge ; so that the principle 
on which his argument rests is altogether gratuitous. He regards 
it, however, as resting upon facts ; for he further. says, ‘1 have» 
found in a great variety of experiments on the seeds of the 
horse-chesnut, bean, and other plants, when vegetating at rest, 
that the vessels and fibres on the under side of the germen inva- 
riably elongated much more rapidly than those on its upper 
side, and thence it follows that the pomt of the germen must 
always turn upwards.” Nor is this increased elongation con- 
fined to the under side of the germens, nor even to the annual 
shoots of trees ; but it occurs and produces the most extensive 
effects inthe subsequent growth of their trunks and branches.” 
_ It is to be regretted that no particular account of these expe- 
riments is given, nor of the way in which the elongation was 
ascertained. But it is certain that this elongation does not 
always take place where a bend exists, so as to make the point 
* Phil. Trans, 1806, Part I, p. 104, 
Vou. XIII. N° IV. R 
