CHAP. XL TBANSMJTTED EFFECTS : PHASEOLUS. 535 



the apex. After 24 h., and again after 32 h. from the commence- 

 ment, four of the cauterised radicles were still horizontal, but 

 one was plainly geotropic, being inclined at 45 beneath the 

 horizon. The five controls were somewhat geotropic after 7 h. 

 20m., and after 24 h. were all strongly geotropic ; being inclined 

 at the following angles beneath the horizon, viz., 59, 60, 65, 

 57, and 43. The length of the radicles was not measured in 

 either set, but it was manifest that the cauterised radicles had 

 grown greatly. 



The following case proves that the action of the caustic by 

 itself does not prevent the curvature of the radicle. Ten radicles 

 were extended horizontally on and beneath a layer of damp 

 friable peat-earth; and before being extended their tips were 

 touched with dry caustic on the upper side. Ten other radicles 

 similarly placed were touched on the lower side ; and this would 

 tend to make them bend from the cauterised side ; and therefore, 

 as now placed, upwards, or in opposition to geotropism. Lastly, 

 ten uncauterised radicles were extended horizontally as controls. 

 After 24 h. all the latter were geotropic ; and the ten with their 

 tips cauterised on the upper side were equally geotropic ; and 

 we believe that they became curved downwards before the con- 

 trols. The ten which had been cauterised on the lower side 

 presented a widely different appearance : No. 1, however, was 

 perpendicularly geotropic, but this was no real exception, for on 

 examination under the microscope, there was no vestige of 

 a coloured mark on the tip, and it was evident that by a mistake 

 it had not been touched with the caustic. No. 2 was plainly 

 geotropic, being inclined at about 45 beneath the horizon; No. 3 

 was slightly, and No. 4 only just perceptibly geotropic; Nos. 5 

 and 6 were strictly horizontal ; and the four remaining ones were 

 bowed upwards, in opposition to geotropism. In these four 

 cases the radius of the upward curvatures (according to Sachs' 

 cyclometer) was 5 mm., 10 mm., 30 mm., and 70 mm. This cur- 

 vature was distinct long before the 24 h. had elapsed, namely, 

 after 8 h. 45 in. from the time when the lower sides of the tips 

 were touched with the caustic. 



Phaseolus multiflorus. Eight radicles, serving as controls, were 

 extended horizontally, some in damp friable peat and some in 

 damp air. They all became (temp. 20-21 C.) plainly geo- 

 tropic in 8 h. 30 m., for they then stood at an average angle of 63 

 beneath the horizon. A rather greater length of the radicle is 

 bowed downwards by geotropism than in the case of Viciafaba, 



