chapter  IX
3 Pages

SENSITIVENESS OF PLANTS TO LIGHT: ITS TRANSMITTED EFFECTS

Uses of heliotropism - Insectivorous and climbing plants not heliotropicSame organ heliotropic at one age and not at another - Extraordinary sensitiveness of some plants to light - The effects of light do not correspond with its intensity - Effects of previous illumination - Time required for the action of light - After-effects of light - Apogeotropism acts as soon as light fails - Accuracy with which plants bend to the light - This dependent on the illumination of one whole side of the part - Localized sensitiveness to light and its transmitted effects - Cotyledons of Phalaris, manner of bending - Results of the exclusion of light from their tips - Effects transmitted beneath the surface of the ground - Lateral illumination of the tip determines the direction of the curvature of the base - Cotyledons of Avena, curvature of basal part due to the illumination of upper part - Similar results with the hypocotyls of Brassica and Beta - Radicles of Sinapis apheliotropic, due to the sensitiveness of their tips - Concluding remarks and summary of chapter - Means by which circumnutation has been converted into heliotropism or apheliotropism.