CHAP. III. OF THE RADICLE OF EAPHANUS. 171 



they grow better and more naturally than in damp 

 air ; and their tips were slightly cauterised on the 

 lower side, brown marks about ^ mm. in length 

 being thus caused. Uncauterised specimens similarly 

 placed became much bent downwards through geo- 

 tropism in the course of 5 or 6 hours. After 8 h. 

 only 3 of the cauterised ones were bowed downwards, 

 and this in a slight degree ; 4 remained horizontal ; 

 and 3 were curved upwards in opposition to geo- 

 tropism and from the side bearing the brown mark. 

 Ten other specimens had their tips cauterised at the 

 same time and in the same degree, on the upper 

 side ; and this, if it produced any eifect, would tend 

 to increase the power of geotropism ; and all these 

 radicles were strongly bowed downwards after 8 h. 

 From the several foregoing facts, there can be no 

 doubt that the cauterisation of the tip of the radicle 

 of this Cucurbita on one side, if done lightly enough, 

 causes the whole growing part to bend to the opposite 

 side. 



Raphanus sativus : Sensitiveness of the apex of the 

 Radicle. We here encountered many difficulties in 

 our trials, both with squares of card and with caustic ; 

 for when seeds were pinned to a cork-lid, many of the 

 radicles, to which nothing had been done, grew irre- 

 gularly, often curving upwards, as if attracted by the 

 damp surface above ; and when they were immersed 

 in water they likewise often grew irregularly. We 

 did not therefore dare to trust our experiments with 

 attached squares of card ; nevertheless some of them 

 seemed to indicate that the tips were sensitive to 

 contact. Our trials with caustic generally failed from 

 the difficulty of not injuring too greatly the extremely 

 fine tips. Out of 7 radicles thus tried, one became 

 bowed after 22 h. at an angle of 60, a second at 40 



