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Show 522 MODIFIED CrRCUl\:INUTATION. Cl!AP.X. have bee~ acq~irecl for the aflvantago of tho plant by the mo(hficatwn of tho over-present movement of cir~umnutation. 'rhis, however, implies that gravitatwn produces some effect on tho younO' tissues sufficient to serve as a guide to the plant. 0 CnAP. XI. SENSITIVENESS TO GRAVITATION. 523 CHAPTER XI. LoCALISED SENSITIVENESS TO G RAVI'l'ATION, AND ITS TRANS:l1IT1'ED EFFECTS. General considerations-Vicin. faba, e{fol'ts of amputating the tips of the radicles-Regeneration of tho tips- Kffects of a short exposure of the tips to geotropic action and their RuhHcquont amputationEffects of o.mputating tho tips obliquely-Effects of cuuterismg the tips-Effects of grease on tlte tips-Pisu11t sativum, tips of' rfldicles rautcrised transversely, and on their npper and lower sidesPhaseolus, cauterisation and grease on fho tips-GossypiumOucurbita, tips cauterised transversely, and on their upper and lower sides- Zea, tips cauterised- Concluding remarks and summary of ch~tpter-Advo.ntagos of the ~cnsibility to g<'otropism being loco.lisecl in the tips of tho radiclcs. CIESIELSKI states* that when tho roots of P.isum, Lens and Vicia were extended horizontally with their tips cut off, they were not acted on by geotropism ; but some days afterwards, when a new root-cap and vegetative point had been formed, they bent themselves 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 tho 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 * 29 ' Abwartskriimmung dur Wurzel,' Inaug. Di sort. Brcslau, 1871, p, • |