Chapter Iii.—Sensitiveness of the Apex of the Radicle to Contact and to

OTHER IRRITANTS. 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—Æsculus, 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.