... not only the organ for light-perception, but also for gravitation. If a seedling is supported horizontally by pushing the apical part (cotyledon) into a horizontal tube, the cotyledon will, according to my supposition, be stimulated gravitationally and a stimulus will be transmitted to the basal part of the stem (hypocotyl) causing it to bend. But this curvature merely raises the basal end of the seedling, the sensitive cotyledon remains horizontal, ... — Darwin and Modern Science • A.C. Seward and Others