their tips cauterised on the upper side were equally geotropic; and we believe that they became curved downwards before the controls.  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 45o 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 curvature was distinct long before the 24 h. had elapsed, namely, after 8 h. 45 m. 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 20o — 21o C.) plainly geotropic in 8 h. 30 m., for they then stood at an average angle of 63o beneath the horizon.  A rather greater length of the radicle is bowed downwards by geotropism than in the case of Vicia faba, [page 536] that is to say, rather more than 6 mm. as measured from the apex of the root-cap.  Nine other radicles were similarly extended, three in damp peat and six in damp air, and dry caustic was held transversely to their tips during 4 or 5 seconds.  Three of their tips were afterwards examined:  in (1) a length of 0.68 mm. was discoloured, of which the basal 0.136 mm. was yellow, the apical part being black; in (2) the discoloration was 0.65 mm. in length, of which the basal 0.04 mm. was yellow; in (3) the discoloration was 0.6 mm. in length, of which the basal 0.13 mm. was yellow.  Therefore less than 1 mm. was affected by the caustic, but this sufficed almost wholly to prevent geotropic action; for after 24 h. one alone of the nine cauterised radicles became slightly geotropic, being now inclined at 10o beneath the horizon; the eight others remained horizontal, though one was curved a little laterally.

The terminal part (10 mm. in length) of the six cauterised radicles in the damp air, had more than doubled in length in the 24 h., for this part was now on an average 20.7 mm. long.  The increase in length within the same time was greater in the control specimens, for the terminal part had grown on an average from 10 mm. to 26.6 mm.  But as the cauterised radicles had more than doubled their length in the 24 h., it is manifest that they had not been seriously injured by the caustic.  We may here add that when experimenting on the effects of touching one side of the tip with caustic, too much was applied at first, and the whole tip (but we believe not more than 1 mm. in length) of six horizontally extended radicles was killed, and these continued for two or three days to grow out horizontally.