Publisher Summary Research on cellulase in the bean plant, Phaseolus vulgaris L. cv. Red Kidney, has led to the discovery of a family of cellulases with differing forms and functions. The development of methods for differentiating cellulase activities made it possible to begin sorting out the functions of the various cellulases. With the purification of the 9.5 cellulase and subsequent production of antibodies to it, the amount of 9.5 cellulase activity vs acidic pl cellulases could be quantitated. It was found that 9.5 cellulase is synthesized de novo in the abscission zone of bean leaves in response to ethylene. Synthesis of 9.5 cellulase is confined to a very narrow band of cells in the abscission zone. The acidic forms of cellulase occur throughout the plant, particularly in young rapidly expanding tissue. These forms appear to be auxin regulated and involved in growth and differentiation. The affinity of 9.5 cellulase has been exploited for its substrate and purified the enzyme on a cellulose column. Hydrolysis of the cellulose does occur to some extent, as reducing sugars are found in the peak fractions containing the purified enzyme. As the acidic cellulases have only been partially purified, their substrate specificity has not been firmly established.