A Technique for taking Successive Shadowgraphs of the Same Seedlings in Growth and Curvature Experiments with Oat Coleoptiles

A method is described for taking successive shadowgraphs ofthe same Avena seedlings, using an orange-sensitive paper andvery low-intensity orange light such that whereas shadowgraphscan be made with one minute's exposure no photo-tropic or growthresponse can be detected as a result of one hour's unilateralexposure of intact seedlings. Phototropic curvatures producedby somewhat higher intensities of red light emphasize the importanceof specifying not only the wave-length but also the intensityand duration of illumination used in experiments with Avenaseedlings. When not subjected to the unilateral illuminationthe seedlings were grown under deep red light (wave-length >0.63 µ) at a total intensity of less than 1/6 foot-candle;it must not be assumed that the technique would be satisfactoryfor seedlings grown in total darkness.