When a plant is rotated on a clinostat, with its axis parallel to the ground, the axis may remain straight. According to Sachs (9), the successive stimuli of gravity compensate each other and, therefore, there is no tropic reaction. Czapek (4) on the other hand, felt that under these conditions, there is no perception of the gravity by the plant and consequently no tropic reaction. In connection with an attempt to study the effect of clinostat rotation on photoperiodism, a special clinostat was

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... built with a large wheel upon which a number of plants could be rotated simultaneously, with the plants anchored near the periphery of the wheel and not at the axis of rotation. Instead of remaining straight, the stems were predominantly bent along the circumference of the circle in the direction of rotation. The studies reported here are an attempt to find the causal factors of this uni-directional bending. Methods & Materials The plants used for the experiments were Xantthium pensylvanicumn, Wallr., grown from seeds obtained in the vicinity of Chicago, Ill. The burs were planted in flats and the seedlings were transplanted 4 to 6 days after emergence into 4-inch pots. These were placed on benches and given 20 hours of light each day until they had six to eight mature leaves, at which time they were used for the experiments. Instead of the standard clinostat, a modified form which we choose to call a rotator was used (see fig la) . It is capable of handling 24 plants at one time. It is driven by a 1/70 hp synchronous electric motor; the 0.75 inch thick plywood turntable was rotated at 1 Received Nov. 13, 1961.