* Elfving has lately described (’Arbeiten des Bot.  Instituts in Würzburg,’ B. ii. 1880, p. 489) an excellent instance of such movements in the rhizomes of certain plants. [page 522]

have been acquired for the advantage of the plant by the modification of the ever-present movement of circumnutation.  This, however, implies that gravitation produces some effect on the young tissues sufficient to serve as a guide to the plant. [page 523]

CHAPTER XI.

Localised sensitiveness to gravitation, and its transmitted effects.

General considerations—­Vicia faba, effects of amputating the tips of the radicles—­Regeneration of the tips—­Effects of a short exposure of the tips to geotropic action and their subsequent amputation—­Effects of amputating the tips obliquely—­Effects of cauterising the tips—­Effects of grease on the tips—­Pisum sativum, tips of radicles cauterised transversely, and on their upper and lower sides—­Phaseolus, cauterisation and grease on the tips—­Gossypium—­Cucurbita, tips cauterised transversely, and on their upper and lower sides—­Zea, tips cauterised—­Concluding remarks and summary of chapter—­Advantages of the sensibility to geotropism being localised in the tips of the radicles.

Ciesielski states* that when the roots of Pisum, 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 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

* ‘Abwartskrümmung der Wurzel,’ Inaug.  Dissert.  Breslau, 1871, p. 29. [page 524]

vegetative point) of the tips of the radicles of the bean (Vicia faba), and placed them horizontally or vertically in damp air, earth, and water, with the result that they became bowed in all sorts of directions.* He therefore disbelieved in Ciesielski’s conclusions.  But as we have seen with several plants that the tip of the radicle is sensitive to contact and to other irritants, and that it transmits some influence to the upper growing part causing it to bend, there seemed to us to be no a priori improbability in Ciesielski’s statements.  We therefore determined to repeat his experiments, and to try others on several species by different methods.