. Biology in America. Biology. 310 Biology in America are not strictly symmetrical they may be assumed to be so for the purposes of the theory. Thus if a Paramoecium be acted upon by an electric current whose direction is oblique to the long axis of its body, the cilia on the side toward the negative pole beat more vigorously than do those on the positive side, and in the opposite direction, causing the animal to turn until it is in line with the current when it swims ahead, toward the negative pole. The stem of a plant turns toward the light, or bends upward, because of a difference in amount
. Biology in America. Biology. 310 Biology in America are not strictly symmetrical they may be assumed to be so for the purposes of the theory. Thus if a Paramoecium be acted upon by an electric current whose direction is oblique to the long axis of its body, the cilia on the side toward the negative pole beat more vigorously than do those on the positive side, and in the opposite direction, causing the animal to turn until it is in line with the current when it swims ahead, toward the negative pole. The stem of a plant turns toward the light, or bends upward, because of a difference in amount of chemical substances on the two sides, and ''this causes a difference in the velocity of chemical reactions be- tween (the two sides)." The organism has no control over its behavior but is so to speak blown about "by every wind that blows" as helplessly as a derelict ship upon the Sagging in a Stem Due to unequal growth on the two sides. From Loeb, "Forced Move- ments, Tropisnis and Animal ; By permission oj J. B. Lippincott Company. But what proof have we that such chemical changes as Loeb asvsumes do occur in the organism? If we suspend a stem of a plant in a horizontal position, it soon bends downward, taking the form of a U. This bending is not due to sagging of the stem as a rope sags, but rather to unequal growth of the two sides, which can be proven by marking equal dis- tances on upper and lower sides by lines of India ink and later measuring the amount of growth occurring between the marks. If the amount of bending in such a stem with leaves attached be compared with that in a stem lacking leaves, it will be found to be much greater in the former due to the greater amount of growth material available, and similarly there is greater bending in a stem furnished with a. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these ill
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