Aesculus hippocastanum: Sensitiveness of the apex of the Radicle.--Bits of
glass and squares of card were affixed with shellac or gum-water to the
tips of 12 radicles of the horse-chestnut; and when these objects fell off,
they were refixed; but not in a single instance was any curvature thus
caused. These massive radicles, one of which was above 2 inches in length
and .3 inch in diameter at its base, seemed insensible to so slight a
stimulus as any small attached object. Nevertheless, when the apex
encountered an obstacle in its downward course, the growing part became so
uniformly and symmetrically curved, that its appearance indicated not mere
mechanical bending, but increased growth along the whole convex side, due
to the irritation of the apex.
That this is the correct view may be inferred from the effects of the more
powerful stimulus of caustic. The bending from the cauterised side occurred
much slower than in the previously described species, and it will perhaps
be worth while to give our trials in detail.
[The seeds germinated in sawdust, and one side of the tips of the radicles
were slightly rubbed once with dry nitrate of silver; and after a few
minutes were allowed to dip into water.
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