Postgenital Carpel Fusion in Catharanthus Roseus (Apocynaceae) Iv. Significance of the Fusion

The ontogenetic and phylogenetic significances of the postgenital carpel fusion in Catharanthus roseus were investigated experimentally. When one of the two carpel primordia was surgically destroyed prior to carpel fusion, the remaining carpel differentiated nevertheless; however, the tissue development on the adaxial (normally fused) carpel face appeared aberrant. Possible reasons for this modified ontogeny are discussed. The suggestion that syncarpy is phylogenetically significant because any pollen tube can potentially reach any ovule was verified in C. roseus by monitoring pollen tube growth following spatially controlled pollinations. The suture formed by the postgenital fusion was no barrier to pollen tube growth, and the pollen tubes rapidly became distributed throughout the stigmatic tissue.