Manner in which radicles bend when they encounter an obstacle in the soil--
Vicia faba, tips of radicles highly sensitive to contact and other
irritants--Effects of too high a temperature--Power of discriminating
between objects attached on opposite sides--Tips of secondary radicles
sensitive--Pisum, tips of radicles sensitive--Effects of such sensitiveness
in overcoming geotropism--Secondary radicles--Phaseolus, tips of radicles
hardly sensitive to contact, but highly sensitive to caustic and to the
removal of a slice--Tropaeolum--Gossypium--Cucurbita--Raphanus--Aesculus,
tip not sensitive to slight contact, highly sensitive to caustic--Quercus,
tip highly sensitive to contact--Power of discrimination--Zea, tip highly
sensitive, secondary radicles--Sensitiveness of radicles to moist air--
Summary of chapter.
IN order to see how the radicles of seedlings would pass over stones,
roots, and other obstacles, which they must incessantly encounter in the
soil, germinating beans (Vicia faba) were so placed that the tips of the
radicles came into contact, almost rectangularly or at a high angle, with
underlying plates of glass.
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