. The dynamics of living matter . LECTURE VII HELIOTROPISM i. THE HELIOTROPISM OF SESSILE ORGANISMS MACHINES which are constructed artificially are arranged in such a manner that the energy which they require is provided by the hand of man. Through the blind play of the forces of nature durable machines can be created only if their supply of energy is regulated automatically. As an example of that type of machine we may men- tion the waterfall. The waterfall is a machine which transforms dis- tance energy into kinetic energy and heat, and the permanency of this machine is guaranteed by the phy
. The dynamics of living matter . LECTURE VII HELIOTROPISM i. THE HELIOTROPISM OF SESSILE ORGANISMS MACHINES which are constructed artificially are arranged in such a manner that the energy which they require is provided by the hand of man. Through the blind play of the forces of nature durable machines can be created only if their supply of energy is regulated automatically. As an example of that type of machine we may men- tion the waterfall. The waterfall is a machine which transforms dis- tance energy into kinetic energy and heat, and the permanency of this machine is guaranteed by the physical conditions that determine the continued flow of water to the cataract. The green plants represent another type of such machines; namely, machines which, among others, transform radiating energy into chemical energy. The permanency of this kind of machines is guaranteed by the presence of an automatic arrangement in such plants, whereby their stems grow toward the light. The automatic turning of the stems of many plants toward the light is called heliotropism. We shall go a little deeper into the analysis of these phenomena, inasmuch as heliotropism and similar phenomena give, to a large extent, an insight into the mechanism of automatic self- preservation of organisms. The stems of many plants in the open grow vertically upward, while the same stems when raised in a room which receives light from only one side grow toward the window. Roots which contribute toward the maintenance of the plant by absorbing the necessary salts from the soil show very frequently (though not always) the opposite behavior. When exposed to light they bend and grow away from the source of light. This behavior is determined only by rays of a certain wave length of the visible spectrum and possibly by some ultraviolet rays. The dark heat rays have no such effects. We do not yet know with the same degree of certainty, as in the case of the process of assimilation, the relative heliotropic efficiency
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