Chap. XI. TRANSMITTED EFFECTS : VICL\- 533 



of geotropism ; 4 were first looked at after 14 h., and one alone 

 of these was slightly geotropic. After 23-21 h., 5 of the 10 were 

 still horizontal, 4 slightly, and 1 decidedly, geotropic. After 

 48 h. some of them became strongly geotropic. The cauterised 

 radicles increased greatly in length, but the measurciiients are 

 not worth giving. 



As five of the last-mentioned cauterised radicles had become in 

 24 h. somewhat geotropic, these (together with three which were 

 still horizontal) had their positions reversed, so that their tips 

 were now a little upturned, and they were again touched with 

 caustic. After 24 h. they showed no trace of geotropism ; whereas 

 the eight corresponding control specimens, which had like- 

 wise been reversed, in which position the tips of several pointed 

 to the zenith, all became geotropic ; some having passed in the 

 24 h. through an angle of 180°, others through about 13-5°, and 

 others through only 90°. The eight radicles, which had been 

 twice caaterised, were observed for an additional day (i.e. for 48 h. 

 after being reversed), and they still showed no signs of geotro- 

 pism. Nevertheless, they continued to gr..w rapidly ; four wei'e 

 measured 24 h. after being reversed, and they had in this time 

 increased in length betweon 8 and 11 mm. ; the other four were 

 measured 48 h. after being reversed, and these had increased by 

 20, 18, 23, and 28 mm. 



In coming to a conclusion with respect to the effects of cauter- 

 ising the tips of these radicles, we should bear in mind, 

 firstly, that horizontally extended control radicles were always 

 acted on by geotropism, and became somewhat bowed down- 

 wards in 8 or 9 h. ; secondly, that the chief seat of the curvature 

 lies at a distance of from 3 to 6 mm. from the tip ; thirdly, that 

 the tip was discoloured by the caustic rarely for more than 

 1 mm. in length ; fourthly, that the greater number of the cau- 

 terised radicles, although subjected to the full influence of 

 geotropism during the whole time, remained horizontal for 24 h., 

 and some for twice as long ; and that those which did become 

 bowed were so only in a slight degree ; fifthly, that the cau- 

 terised radicles continued to grow almost, and sometimes quite, 

 as well as the uninjured ones along the part which bends most. 

 And lastly, that a touch on the tip with caustic, if on one side, 

 far from preventing curvature, actually induces it. Bearing all 

 these facts in mind, we must infer tbat under normal conditions 

 the geotropic curvature of the root is due to an influence trans- 

 mitted fi'om the apex to the adjoining part where tho bending 



