Elongation responses of the oat shoot to blue light, as measured by capacitance auxanometry.

An auxanometer based on capacitance micrometry is described. It does not require light or contact with the plant, and will detect changes in length of the Avena coleoptile of 1 micrometer in 3 to 5 seconds. The field employed, 1 kilohertz at a gradient of 5 volts per centimeter, does not affect the growth rate of the coleoptile. Vertical illumination with blue light at fluences of 1 to 50 ergs.cm(-2) cause an accelerated rate of coleoptile extension, beginning within 10 min after exposure. At higher exposures, the previously described growth inhibition becomes dominant.