during which the cauterised specimens were observed.  With Vicia faba 19 radicles were cauterised; 12 remained horizontal during 23-24 h.; 6 became slightly and 1 strongly geotropic.  Eight of these radicles were afterwards reversed, and again touched with caustic, and none of them became geotropic in 24 h., whilst the reversed control specimens became strongly bowed downwards within this time. [page 542] With Pisum sativum, five radicles had their tips touched with caustic, and after 32 h. four were still horizontal.  The control specimens were slightly geotropic in 7 h. 20 m., and strongly so in 24 h.  The tips of 9 other radicles of this plant were touched only on the lower side, and 6 of them remained horizontal for 24 h., or were upturned in opposition to geotropism; 2 were slightly, and 1 plainly geotropic.  With Phaseolus multiflorus, 15 radicles were cauterised, and 8 remained horizontal for 24 h.; whereas all the controls were plainly geotropic in 8 h. 30 m.  Of 5 cauterised radicles of Gossypium herbaceum, 4 remained horizontal for 23 h. and 1 became slightly geotropic; 6 control radicles were distinctly geotropic in 7 h. 45 m.  Five radicles of Cucurbita ovifera remained horizontal in peat-earth during 25 h., and 9 remained so in damp air during 8 ½ h.; whilst the controls became slightly geotropic in 4 h. 10 m.  The tips of 10 radicals of this plant were touched on their lower sides, and 6 of them remained horizontal or were upturned after 19 h., 1 being slightly and 3 strongly geotropic.

Lastly, the tips of several radicles of Vicia faba and Phaseolus multiflorus were thickly coated with grease for a length of 3 mm.  This matter, which is highly injurious to most plants, did not kill or stop the growth of the tips, and only slightly lessened the rate of growth of the whole radicle; but it generally delayed a little the geotropic bending of the upper part.

The several foregoing cases would tell us nothing, if the tip itself was the part which became most bent; but we know that it is a part distant from the tip by some millimeters which grows quickest, and which, under the influence of geotropism, bends most.  We have no reason to suppose that this part is injured by the death or injury of the tip; and it is certain [page 543] that after the tip has been destroyed this part goes on growing at such a rate, that its length was often doubled in a day.  We have also seen that the destruction of the tip does not prevent the adjoining part from bending, if this part has already received some influence from the tip.  As with horizontally extended radicles, of which the tip has been cut off or destroyed, the part which ought to bend most remains motionless for many hours or days, although exposed at right angles to the full influence of geotropism, we must conclude that the tip alone is sensitive to this power, and transmits some influence or stimulus to the adjoining parts, causing them to bend.  We have direct evidence of such transmission;