An Oxidation and Adsorption Reaction for Differentiating the Endodermis and the Collenchyma

Abstract

A method is presented for a study of the endodermis and collenchyma in vascular plants. The method is useful in histologically isolating these tissues, particularly where the accepted anatomical features and the usual staining reactions are not definitive. The exclusive oxidation of the leuco (reduced) form of common redox indicators to the oxidized and colored form by the endodermis may be induced by treating fresh free-hand or freezing microtome sections with various alkaline salts at pH 8.5 to 9.0. Placing sections in sodium borate or sodium selenite induces an immediate oxidation of a tincture of gum guaiac in the endodermis and after several minutes a gradual and weak oxidation in the collenchyma. Addition of glycerol to sections which show oxidation in the endodermis induces a localized adsorption of the oxidized indicator in the collenchyma. The endodermis and the collenchyma may be differentiated best by oxidation and adsorption respectively by means of sodium selenite, guaiac and glycerol in the order given. The collenchyma in roots has not been defined to date, and the reactions described introduce a new method of study for this tissue. By treating sections with boric acid a gradient in the guaiac reaction appears in the cortex.