A clinostat is a device which is used to negate the effects of gravitational pull on plant growth. A single axis clinostat consists of a disc attached to a motor, originally clockwork but usually electric nowadays. The disc is held vertically and the motor rotates it slowly at rates in the order of one revolution per minute. A plant is attached to the disc so that it is held horizontally. The slow rotation means that the plant experiences a gravitational pull that is averaged over 360 degrees, thus approximating a weightless environment. Clinostats have also been used to cancel out effects of sunlight and other stimuli besides gravity.
A single axis clinostat only produces the weighlessness effect along its axis of rotation. A 3D or two axis clinostat, can average gravitational pull over all directions.