The cotyledons of Cucurbita maxima provide a system which permits the isolation of chloro-plasts in various states of structural disintegration. These states are defined and corrlated with the morphological appearance of the cotyledon and its electron microscopic and biochemical parameters. Removal of growth above the cotyledons results in cotyledons whose chloroplasts do not change in pigment composition. The connection between light-harvesting apparatus and electron transport components remains intact in these plastids while the electron transport chain undergoes age-induced alterations. The implications of these observations on studies of structure-function relationships in photosynthesis are discussed.