THE most reliable method for distinguishing quantitatively between the branched and unbranched components of starch has depended upon the degree of hydrolysis to maltose effected by an amylase of the beta-type. The branch points in a ramified structure (amylopectin) represent obstructions which the enzyme cannot surmount in the course of its normal function of progressively splitting off maltose units, one at a time, from non-reducing chain-ends. In consequence, the action of beta-amylase on amylopectin ceases at about 50 per cent conversion to maltose. Obviously a chain molecule with no branches would be completely converted into maltose, and indeed in the earlier literature amylose is more or less defined as that component of starch which, on beta-amylolysis, yields 100 per cent maltose. Actually, in our experience, an amylose of this degree of purity (total absence of branching) has not been obtained.