A transducer was developed to record the circadian movement of the individual leaflets in Oxalis regnellii Mig. The method can easily be adapted to measure other kinds of plant movements as well. It is based on the detection of the shadow each leaflet casts on the small side of a specially formed Perspex plate. The light is guided through the Perspex and collected by a phototransistor, which provides an electrical signal that is proportional to the light intensity falling onto it. The output signal can be made a linear function of the leaf angle. This equipment was used in experiments to study the coupling between the 3 leaflets in Oxalis. Pulses of 4 h of red light were given to one of the leaflets, the two others were shielded from the light. A phase response curve was determined for each leaflet, but there was no significant difference in the phase response between the 3 leaflets. Experiments were also made in which the 3 leaflets were separated physically by cuts along the petiole between the pulvini. In this case ultradian oscillations were observed.

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A measurement system based on a photodiode array technique is presented, together with some results from recordings of phototropic responses of Avena sativa L. (cv. Seger I) coleoptiles. A commercial photodiode array (RL‐256G) was used, controlled by a likewise commercial control board RC‐301. Electronic circuits were built to connect the control board to the interface card IO‐801 of an Apple IIe microcomputer. The circuits constitute a fast temporary memory, which mainly contains two shift registers and two timers. Programs, which control the measurements, have been written and are presented. Detailed recordings of blue light induced phototropic movements are presented: resolution and other features of the equipment are discussed.

A photodiode array method has been used to record automatically minute lateral movements of Avena sativa L. (cv. Seger I) coleoptiles in a static electric field. The electric fields, 600 or 5000 V cm−1 did not cause any significant movement of the coleoptiles, in contrast to reports in the literature. Likewise, in experiments where photographic recordings were made, no significant movements were found.