formed a loop.
Four others were considerably curved from the squares after 20 h., and
three of them became hooked, with their tips pointing to the zenith,--one
after 29 h. and the two others after 44 h. By this latter time a sixth
radicle had become bent at a right angle from the side bearing the square.
Thus altogether six out of the ten secondary radicles were acted on, four
not being affected. There can, therefore, be no doubt that the tips of
these secondary radicles are sensitive to slight contact, and that when
thus excited they cause the upper part to bend from the touching object;
but generally, as it appears, not in so short a time as in the case of the
first-formed radicle.
SENSITIVENESS OF THE TIP OF THE RADICLE TO MOIST AIR.
Sachs made the interesting discovery, a few years ago, that the radicles of
many seedling plants bend towards an adjoining damp surface.* We shall here
endeavour to show that this peculiar form of sensitiveness resides in their
tips. The movement is directly the reverse of that excited by the irritants
hitherto considered, which cause the growing part of the
* 'Arbeiten des Bot.
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