A simple apparatus is described which enables records to be made of the nutational movements of small amplitude exhibited by seedling plants. The apparatus described has a resolution of o.1 mm and 5 minutes. The recording system is capable of recording over periods of up to 24 hours' duration automatically. Using this apparatus, numerous recordings have been made of the nutation of runner-bean seedlings. The movement exhibited is considered to be the result of a periodic, oscillatory movement, namely nutation, upon which are superimposed linear movements caused by tropic responses or random growth irregularities. The apparatus has been found especially useful for the study of the periodicity of nutation, and a study of the variability of this parameter in the nutation of the bean seedling at a constant temperature has been made as an essential prerequisite for the study of the effect of experimental treatments. The variability has been shown to be high, even within the same plant.