portion of the corpuscle in which it is immersed; yet on its activity as spread in this infinitesimal quantity through the leaves the whole organic world, animal as well as vegetable, depends.[9] Utilizing the energy which comes through space from the sun, it builds up organic compounds; from the energy thus stored comes all the varied life and vital movement which fill our world--the opening of flowers, the hum of insects, the march of armies, and our own restless thought; while its work in the distant past, laid by in coal and oil, warms our houses and drives our trains, factories, and steamships. The work of the living chlorophyll accomplished, the food materials produced by its agency are sent by the pipe-system to all parts of the plant, for present use, or to be stored in root, stem, or leaf for future requirements. Nor is our plant the passive, motionless thing that it may appear to be in comparison with animals and their larger movements. Active motion, local and general, though usually of relatively small amount, accompanies all plant-growth. Throughout root, stem, leaf, and flower transference of material is going forward vigorously. The root hairs and stomata are working at high pressure; the chlorophyll never ceases its activities while daylight lasts. Externally, the growing branches, leaves, and flowers also display incessant movement, sweeping the air in small circles, or in the case of climbing plants in curves of considerable amplitude. Alterations of illumination or of temperature produce other movement--bendings towards or away from light, the drooping of leaves and closing of flowers at nightfall, and so on. All these phenomena of growth and movement culminate in the production of flowers, and in the remarkable developments by which, through the agency of pollen and ovule, a new generation is produced. CHAPTER VI PLANTS AND MAN