Ohap. XI. SBNSITIVENFSS TO GRAVITATION. 523 



CHAPTER XL 



LOOALISED SeNSITIVEXESS Ta GRAVITATION, AND ITS TRANSMITTED 



EFPEOTd. 



General considerations— 'Vioia faba, effects of amputating the tips of 

 the radicles — l?egeneration of the tips — Effects of a short exposure 

 of the tips to geotvopio action and their subsequent amputation — 

 Effects of amputating the tips obliquely — Effects of cauterising the 

 tips — Effects of grense ontlie tips — Pisum sativum, tips of radicles ■ 

 cauterised transversely, and on their upper and lower sides — 

 Phaseolus, cauterisation and grease on the tips — Gossypium — 

 Cuourbita, tips cauterised transversely, and on their upper and. 



. lower sides — Zea, t^ps cauterised — Concluding remarks and 

 summary of chapter — Advantages of the seusibilily to geotropism 

 being localised in tlie tips of the radicles. 



CiESiBLSKi states * that when the roots of Pisum, 

 Lens and Yicia were extended horizontally with their 

 tips cut oif, they were not acted on by geotropism ; 

 but some days afterwards, when a new root-cap and 

 vegetative point had been formed, they bent them- 

 selves perpendicularly downwards. He further states 

 that if the tips are cut off, after the roots have been 

 left extended horizontally for some little time, but 

 before they have begun to bend downwards, they may 

 be placed in any position, and yet will bend as if still 

 acted on by geotropism ; and this shows that some 

 influence had been already transmitted to the bending 

 part from the tip before it was amputated. Sachs 

 repeated these experiments ; he cut off a length of 

 between '05 and 1 mm. (measured from the apex of the 



• ' Abwartskriimmung der Wurzel,' luaug. Dissert. Breslau. 1871, 

 p. 29. 



