Gelatinized root-starch granules possess a peripheral membrane containing phosphoric-acid ester. This has led some investigators to infer that the natural ungelatinized granule also possesses such a membrane. If this be so, it follows that the P2O5 percentage in the small granules of a given sample should be greater than in the large granules, provided the thickness of the hypothetical membrane of the two sorts of granules is about the same.There are two pertinent observations in the literature. Fernbach1 found the small-sized granules to contain decidedly more P2O5 than the large-sized ones in the same sample of potato starch. He concluded, however, that the granule consists of a nucleus rich in phosphorus upon which are superimposed layers of phosphorus-free material. Kavcic2 determined the P2O5 content of starch from 4 potato varieties with granules of different average diameters. While his figures indicate a tendency for the P2O5 percentage to increase as the average granule size decreases, the differ...