Plastids of the Avena Coleoptile

Abstract

PHOTOTROPIC curvature of the Avena coleoptile may, for reasons which have been summarized elsewhere1, be mediated through the plastids. Geotropic curvature may have a similar basis, for it has long been thought2,3 that the geotropic responses of both shoots and roots are mediated by special starch grains or ‘statoliths’, and these in fact are plastids in which relatively large amounts of starch have been deposited. It is thus worth considering that the many similarities between these two types of tropism may have an anatomical basis. For this reason a closer study has been made of the plastids of the etiolated Avena coleoptile. The observations have been made with the light and phase microscope, utilizing either fresh material vitally stained with neotetrazolium chloride, or microtome sections fixed in chrome-acetic-formalin and embedded and sectioned in ‘Carbowax’. (We wish to thank Prof. R. H. Wetmore and Dr. J. Riopel for assistance and for putting at our disposal the newly developed ‘Carbowax’ method.) Principal attention has been directed to the most apical part of the coleoptile.