STIPULES IN SOME MEMBERS OF THE VITACEAE: RELATING PROCESSES OF DEVELOPMENT TO THE MATURE STRUCTURE

Abstract

The development of stipules especially their spatial and temporal pattern of initiation in relation to the leaf was investigated in Vitis riparia Michx., cv. Concord, Parthenocissus tricuspidata (Sieb. & Zucc.) Planch., Cissus oblonga (Benth.) Planch., Cissus hypoglauca (F.v.M.) A. Gray, and Cissus rhombifolia Vahl. Early initiation is characterized by the occurrence of a single primordium with a wide insertion on the flank of the shoot apex. Distinguishing between stipule primordia and the leaf primordium is impossible at this early stage. Distinct primordia can only be seen in later stages of development. At maturity, the stipules occupy free lateral positions. Developmental processes such as timing of initiation and zonal growth seem to play an important role in early development. In five of the six taxa examined in this study, the early initiation of stipules, their close association with the leaf and also their faster relative rate of growth during early development appear to give them a characteristic protective function. In contrast, C. rhombifolia stipules are initiated later than the leaf and seem to develop at a slower rate than the leaf proper. Consequently, they never enclose their associated leaf but instead cover the next youngest leaf. Many different criteria are used to distinguish the broad category of stipules, and therefore many interpretations have been made depending on the type of approach that is used. This study attempts to look at stipules in terms of developmental processes and demonstrates a more accommodating leaf/stipule concept which provides a clearer comprehension of the nature of the stipule.