THE TRANSMITTING TRACT IN GLADIOLUS. I. THE STIGMA AND THE POLLEN-STIGMA INTERACTION

The stigma papillae in Gladiolus are of the “dry” type and are highly vacuolated cells with an organelle-rich peripheral cytoplasm. The cell wall of each papilla is overlain by a distinctive cuticle possessing an irregularly scalloped inner margin. Between the cell wall and cuticle is a layer of amorphous sub-cuticular material. Lipids are detected on the papilla surface. A pollen grain will hydrate and germinate only on a papilla and not on any other (non-papillate) portion of the stigma. The pollen tube penetrates the papilla cuticle, which is forced away from the papilla cell wall by sub-cuticular pollen tube growth. As the cuticle lifts away, the sub-cuticular material disperses. At the base of the papilla, the pollen tube grows onto the adaxial non-papillate surface of the stigma lobe. At this site, the cuticle has been lifted away from the underlying cells by release of a mucilaginous substance from the latter, and the pollen tube grows within this substance beneath the detached cuticle. The cytological features of Gladiolus papillae are compared with other stigma papillae described in the literature. Also, a review of the literature, as well as some of the findings of the present study, suggest that certain prevalent interpretations of dry stigma structure and function may be open to question.