Carpel Development, Anatomy, and Function in the Reproductive Process in Ornithogalum caudatum (Liliaceae)

Abstract

In Ornithogalum , carpel development begins with the initiation by a basal meristem of domeshaped carpel primordia. These primordia grow primarily by cell expansions rather than by cell division and addition of new cells. Centripetal infolding and fusion of carpels along, their abaxial surface forms septa which define the ovarian locules. Fusion does not occur along the entire suture, however, and septal nectaries develop in the chambers where the two epidermal layers do not fuse. These septal nectaries then secrete exudate at anthesis. The distal portion of the carpels develops into a hollow style terminated by a dry, papillate stigma. In the carpels proper, three types of idioblastic cells occur: one type contains calcium oxalate raphide crystals, another one contains a carbohydrate-protein complex, and the third type, found only in cells of the abaxial epidermis, contains lipotubuloids. Carpellary vasculature consists of one dorsal, two ventral, and two lateral veins, plus numerous small interconnecting veins which differentiate shortly after fertilization and mature during embyogenesis. Stomates and a multi-layered chlorenchyma develop during embryogenesis also. Carbohydrate-protein storage complexes and lipotubuloids are catabolized during later stages of seed maturation, presumably to be used in seed development. Also at this time, the outer wall of the adaxial epidermal cells thickens extensively. As dehiscence approaches, remaining contents of carpellary cells, including raphide crystals, are catabolized and mobilized out of the carpels leaving a reticulum of cell walls. Walls eventually dry and, when stress becomes great enough, thickened inner walls of adaxial epidermis cells roll inward causing the carpels to separate along their suture lines.