Page:Popular Science Monthly Volume 38.djvu/45

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35
THE ROOT- TIP.

the rim of a wheel, and this, placed in a box sufficiently warm and damp, was made to turn in a vertical plane at the rate of one hundred and fifty revolutions a minute. After a few days, the parts of the seedlings were found to be in the position shown in

PSM V38 D045 Gravity and centrifugal force influencing plant growth.jpg

Fig. 4. — Diagrams illustrating Knight's Experiments. A, wheel rotating horizontally; the plants grow under the combined influence of gravity arid centrifugal force. B, wheel rotating vertically; the direction of growth is determined by centrifugal force alone. (Vines.)

Fig. 4, b. Fig. 4, a, shows the position assumed by seedlings placed under conditions entirely similar, except that the wheel was made to turn horizontally. Since both gravity and centrifugal force