MODIFIED CIRCUMNUTATION: SLEEP OR NYCTITROPIC MOVEMENTS, THEIR USE: COTYLEDONS
This chapter shows that with various plants the tip of the radicle is alone sensitive to geotropism; and that when thus excited, it causes the adjoining parts to bend. Radicles of Vicia faba plant were extended horizontally either over water or with their lower surfaces just touching it. The chapter explains analogous and more striking experiments with Pisum sativum and Cucurbita ovifera. In Ciesielski's experiments the radicles could not have grown very irregularly, for if they had done so, he could not have spoken confidently of the obliteration of all geotropic action. As the tip of the radicle has been found to be part which is sensitive to geotropism in the members of such distinct families as the Leguminosae, Malvaceae, Cucurbitaceae and Gramineae, infer that this character is common to the roots of most seedling plants. Finally, the fact of the tip alone being sensitive to / the attraction of gravity have an important bearing on the theory of geotropism.