Results of histochemical tests performed on fresh root tissue of Ranunculus acris provide the following information on the chemical nature of the root endodermis: (i) the Casparian strip is impregnated with lipid and possibly lignin, (ii) the suberin lamellae stain positively for lipid and phenols with free hydroxyl groups, and (iii) the tertiary wall contains alternating bands of lignin and cellulose.At the ultrastructural level, phenolic 'globules' present in vacuoles of adjacent cortical cells increase in size by accretion of flocculent material and the addition of dispersed granular material through the apparent fusion of smaller vacuoles with the large central vacuole. Globules adhering to fragments of the tonoplast membrane are clearly seen with the SEM.The ferric chloride test for catechol-type phenols at the TEM level proved useful in categorizing phenolic compounds present in intercellular spaces, in walls and vacuoles of cortical cells, surrounding starch grains in amyloplasts, and in the cytoplasm of endodermal cells. Prominent plastids containing large deposits of lipid, osmiophilic material, thylakoid membranes, and starch are seen to be a major constituent of cytoplasm in endodermal and cortical cells.