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