Correlation of microsporangial and megasporangial differentiation along racemes of Phytolacca americana L. (Phytolaccaceae)

Both quantitative and qualitative data were obtained for anthers and ovules throughout the lengths of flowering Phytolacca americana (pokeweed) inflorescences. Comparative data were collected for micro‐and megasporangia at seven different locations along the lengths of 20 cm racemes. Each location represented a different developmental stage, from sporangial initiation through full differentiation, along the indeterminate racemes. Reproductive biology of pokeweed anthers, as recognized by inflorescence analysis, was most promoted in development between 4 cm (stage 1) and 5 cm (stage 2) from the terminus of inflorescences. Sporogenous cells first differentiated and stamen cell number quadrupled in stage two. Mitotic divisions, within anther subsurface cells, continued throughout all seven inflorescence stages, while divisions slowed between 6.2 cm (stage 4) and 7 cm (stage 5) from the terminus in anther surface cells. To regulate ovule development maximally, by the treatment of inflorescences, one should manipulate older, more basal flowers (and thus older developmental stages) in excess of 11.6 cm (stage 6) from the terminus. Megasporocytes were initiated and a %fold increase in ovule cell number occurred during stage 6. Similar to anthers, mitosis continued throughout the length of racemes in nucellar cells. Ovule surface cells, however, became mitotically quiescent 11.6 cm (stage 6) from the terminus of racemes.