HETEROBLASTIC SEQUENCE AND LEAF DEVELOPMENT IN LEEA-GUINEENSIS

The leaves initiated at successive nodes in the heteroblastic series i n Leea guineensis seedlings become progressively more complex in const ruction. Leaves at the first four nodes are simple and are followed by transitional forms between nodes 5 and 7. These transitional leaf for ms are compound in nature, and intermediates such as deeply lobed leav es are not observed. At successively higher nodes, the compound nature of the leaves becomes progressively more complex. The most common seq uence of leaf morphologies is simple (nodes 1-4), trifoliate to pinnat e (nodes 5-7), bipinnate (by node 8), and tripinnate (by node 11). The developmental morphology of the simple leaves in the sequence was mar kedly different from the compound leaves that followed. However, the e arly stages of development of the compound leaves, regardless of their degree of complexity, were very similar. Therefore, there appears to be a striking developmental distinction between the simple leaves and the compound leaves in the sequence. Simple leaf primordia become cent rally concave and assume a characteristic folded appearance, whereas c ompound leaves have up to three orders of branching and are structural ly more complex. However, compound leaves of different levels of compl exity seem to share certain developmental features. At its maximum, th e compound nature of the leaf can best be described in terms of subuni ts of seven leaflets. Thus, the complexity of the leaf can be viewed a s a reiteration of the basic unit. The increase in compound leaf compl exity does not alter the rate of leaf production.