which indicated that it unlikely existed in more than every tenth cluster. A comparison of the numbers of building blocks obtained experimentally at 28 DAA with those calculated from the modelare indicated in Table 5; the numbers show a fairly good correlation, considering that a single illustration represents the averagestructure of what is probably a very complex mixture of cluster structures. There is also a good agreement between the numbers of chains of different categories obtained experimentally and those inthe model.The cluster size and number of chains (Table 1) were larger at theend of pre-physiological maturity (28 DAA) than at maturity. The number of the small building blocks with only two chains (group2) was also larger at 28 DAA (Tables 4 and 5), which suggested atrimming of the chains during the period between 28 DAA and 49DAA. Such trimming was originally suggested by Ball et al. (1996)based on the fact that phytoglycogen, which is a highly branched glucan polymer in isoamylase deficient plants (e.g., su2 maize), doesnot crystallize and form granules as normal amylopectin does. Ballet al. (1996) considered phytoglycogen a pre-cursor of amylopectin,which has to be trimmed