there is an overlap between the functions of a storage organ and a perennating organ but they are in principle different see raunki r plant life form for a classification of perennating organs resting buds are a perennating organ but not a storage organ the stem body of a cactus is generally regarded as having been modified to act as a water storage organ but it's not a perennating organ in that it's not what the cactus dies back to in an adverse period there could usefully be some cross referencing which i will attempt