542 SENSITIVENESS TO GRAVITATION. Chap. XI. 



With Pisun sativum, five radicles had their tips touched 

 with caustic, and after 32 h. four were still horizontal. 

 The control specimens were slightly geotropic i\\ 

 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 geotropisra ; 2 were 

 slightly, and 1 plainly geotropic. With Phaseolus 

 muUiflorus, 15 radicles were cauterised, and 8 re- 

 mained horizontal for 24 h. ; whereas all the controls 

 were plainly geotropic in 8 h. 30 m. Of 5 cauterised 

 radicles of Gossypium herhaeeum, 4 remained horizontal 

 for 23 h. and 1 became slightly geotropic ; 6 control 

 I'adicles were distinctly geotropic in 7 h. 45 m. Five 

 radicles of Cueurbita ovifera remained horizontal in 

 peat-earth during 25 h., and 9 remained so in damp 

 air during 8=^ h. ; whilst the controls became slightly 

 geotropic in 4 h. 10 m. The tips of 10 radicals of this 

 plant were touched on their loicer 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.faha and 

 Phaseolus muUiflorus 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 certair 



