The physical basis of gravity stimulus nullification by clinostat rotation.

The question of how rotation on a horizontal axis clinostat removes plants from the influence of the gravitational stimulus is answered. It is shown that appropriate horizontal axis clinostat rotation restricts the fall of intracellular particles to a quasi-circular path such that the position of the particle remains virtually stationary within cells. The displacement of the path of fall, due to centrifugal force, is then considered, and a method of determining the optimal rotation rate is developed from physical principles. This method selects the rotation rate which minimizes the volume of cytoplasm through which particles pass under the joint influence of centrifugal and gravitational forces. With the recognition that single axis clinostats are ineffective with large plants or for long experiments, a new type of clinostat is proposed on which intracellular conditions can be rendered virtually identical to those of plants in satellite free fall regardless of plant size or duration of experiment.It is shown that most low gravity biological responses can be studied using clinostats with only occasional satellite free fall experiments for verification. It is further inferred that most of these responses can be effectively and economically studied by computer simulation.