Old field succession in Oklahoma has been reported to involve four stages of development: pioneer weeds, annual grass, bunch grass, and mature prairie. This sequence has been the basis for a number of analyses of grassland structure and function, but has never been documented on a single site. We used multivariate techniques to study succession on three permanent plots with different initial plowing treatments in a central Oklahoma grassland. Only two of the four hypothesized stages could be identified: pioneer weeds and mature prairie. The intervening vegetation development was heterogeneous and unpredictable. Convergence was evident in only a general manner in that all plots are currently being invaded by shrubs and some tree species. Thus, succession on these plots has advanced beyond prairie to shrub-grassland and we predict that upland forest trees may eventually dominate the site. Succession from pioneer weeds beyond prairie to shrub-grassland has been very rapid. Fire suppression may have contributed to these rapid vegetation changes. Finally, no trends in diversity, evenness, or total number of species were evident during succession.

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The pollination of Paspalum dilatatum was studied in south‐central Oklahoma during the summer of 1979. Pollen was liberated between 0700–0900 hr except on humid mornings (RH ≤ 80%), when there was a delay of 2–3 hr and a reduction in the total air‐borne pollen concentration. A rapid decrease in air‐borne pollen concentration with distance from the source results from: 1) individual pollen grains larger (50–70 μ in diam) than typical wind‐pollinated plants, and 2) some pollen dispersed as clusters of grains. Several floral characters of P. dilatatum led to a hypothesis that this perennial grass may be entomophilous as well as anemophilous. Not only were the pollen grains larger than most other wind‐pollinated taxa but the species produced fewer than 2,500 pollen grains per ovule. Three additional observations corroborate this view: 1) solitary bees (Halictidae) actively collect pollen during the morning, 2) the number of pollen grains per stigma was significantly (P < 0.001) greater on racemes exposed to both wind and bees than on racemes exposed only to wind, and 3) the combination of bees and wind as pollinators significantly (P < 0.001) increased seed set compared to wind alone.