. A textbook of botany for colleges and universities ... Botany. GROWTH AND MOVEMENT 433 cease entirely. When the stimuli recur very frequently, the responses become for a time combined, so that the organ assumes a fixed position unlike the unstimulated one. This quite resembles the condition of a muscle in tetanus, as can be seen by comparing the records in fig. 672. After a period of tetanus, however, the reactions cease until rest from excitation permits recovery. If stimulation, too brief to produce the. Fig. 671. — Uniform electrical response in radish lo repeated stimulation. — After Bos
. A textbook of botany for colleges and universities ... Botany. GROWTH AND MOVEMENT 433 cease entirely. When the stimuli recur very frequently, the responses become for a time combined, so that the organ assumes a fixed position unlike the unstimulated one. This quite resembles the condition of a muscle in tetanus, as can be seen by comparing the records in fig. 672. After a period of tetanus, however, the reactions cease until rest from excitation permits recovery. If stimulation, too brief to produce the. Fig. 671. — Uniform electrical response in radish lo repeated stimulation. — After BosE. end reaction, be repeated at proper intervals, the separate effects be- come combined and suffice presently to call forth the end reaction. This summation of stimulation seems to be a sort of tetanic piling up of the earlier excitations of the series, which finally becomes sufficient to transmit its effects to the active region. Fig. 672. — Records of tetanic contraction in muscle (a, i) and in style of Datura (c, d): a, c, incomplete; b, d, more complete. — After BoSE. Reaction time. — Some time elapses between the beginning of stimu- lation and the end reaction, and this is appropriately called reaction time. Whereas in animals this is usually measured by a fraction of a second, in plants it is much longer, occasionally a few seconds, but often minutes or even hours. This tardiness is due not so much to a low degree of sensitiveness, for the first reaction (perception) takes place almost instantly, as to slow propagation and especially to the sluggish- ness of the mechanism of growth. By contrast, turgor mechanisms usu- ally respond quickly. Naturally the reaction time is made up of the perception time (a small fraction of a second), the transmission time (the rate varies commonly from o to 4 cm. per second), and the growth time, which is far the greater part of the whole Please note that these images are extracted from scanned page images that may have
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