CHAP. XL TRANSMITTED EFFECTS : CONCLUSION. 5<il 



off the tip of a horizontally extended radicle does not 

 prevent the adjoining parts from bending, if the tip 

 has been previously exposed for an hour or two to the 

 influence of geotropism. The tip after amputation is 

 sometimes completely regenerated in three days ; and 

 it is possible that it may be able to transmit an 

 impulse to the adjoining parts before its complete 

 regeneration. The tips of six radicles of Cucurbita 

 ovifera were amputated like those of Vicia faba ; and 

 these radicles showed no signs of geotropism in 24 h. ; 

 whereas the control specimens were slightly affected 

 in 5 h., and strongly in 9 h. 



With plants belonging to six genera, the tips of the 

 radicles were touched transversely with dry caustic ; 

 and the injury thus caused rarely extended for a greater 

 length than 1 mm., and sometimes to a less distance, as 

 judged by even the faintest discoloration. We thought 

 that this would be a better method of destroying the 

 vegetative point than cutting it off ; for we knew, from 

 many previous experiments and from some given in 

 the present chapter, that a touch with caustic on one 

 side of the apex, far from preventing the adjoining 

 part from bending, caused it to bend. In all the 

 following cases, radicles with uncauterised tips were 

 observed at the same time and under similar circum- 

 stances, and they became, in almost every instance, 

 plainly bowed downwards in one-half or one-third of 

 the time during which the cauterised specimens were 

 observed. With Vicia faba 19 radicles were cau- 

 terised ; 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 geo- 

 tropic in 24 h., whilst the reversed control specimens 

 became strongly bowed downwards within this time. 



