| The reproductive biology of Cornus florida L. (Cornaceae) was investigated using light, fluorescence and electron microscopy, controlled pollinations, and field observations. Five floral stages were identified based on petal, anther, nectary, and stigma characteristics. Fertility of the floral stages ranged from 14-90%. Fruit set was highest in stage 3 flowers in 1995 (90%) and 1996 (80%) and in stage 4 flowers in 1997 (79%). Duration of the flower opening period was 10 days (1996) and 23 days (1997). Mean temperatures of the flower opening period were 16.9{dollar}spcirc{dollar}C (1996) and 11.9{dollar}spcirc{dollar}C (1997). Natural fruit set was 6.1% (1996) and 2.5% (1997). Pollen germination was 47-51% after 1 hr incubation on 10% sucrose-1% agar, pH 6.0, in a humid, sealed container at 30{dollar}spcirc{dollar}C. The mean dimensions of dehydrated pollen grains were 47 {dollar}mu{dollar}m (polar axis) and 25 {dollar}mu{dollar}m (equatorial diameter). The pistil consisted of one stigma, one style, and a bilocular, inferior ovary. Unicellular papillae occupied ca. half of the stigmatic surface and extended into a groove. The style contained numerous vascular traces and a centrally located stylar canal that was shaped like an inverted, flattened funnel. The canal cells were cylindrical-to-cubical secretory cells. From 1994-1996, floral initiation began in July, and flowers were well developed in 6-7 weeks. Pollen grains were present only in anthers {dollar}>{dollar}1.0 mm long and in inflorescence buds {dollar}>{dollar}5.3 mm wide. Floral development required ca. 9 months, fruit development required ca. 6.5 months, and the complete process required ca. 15.5 months. Self- and cross-pollen adhered to the stigma, germinated, and pollen tubes were visible in the stylar canal 2 days post-pollination. Cross-pollen tubes reached the upper region of the ovary 4 days post-pollination and entered the micropyle 8 days post-pollination. No self-pollen tubes were observed in the distal portion of the stylar canal or in the ovary. These results suggest that the self-incompatible reactions were restricted to the stylar canal. The center flowers of the third, fifth, and seventh rows opened first in 21 of 24 monitored inflorescences. These studies contribute basic information that should aid in future reproductive and breeding experiments. |
