WPC 2 B V P Z Courier 10cpi ? x x x , Z x 6 X @ 8 ; X @ HP DeskJet 500 HPDES500.PRS x @ x X , , 0 FX @ #| x 2 B V P Z Courier 10cpi ? x x x , x 6 X @ 8 ; X @ HP DeskJet 500 HPDES500.PRS x @ x X , , 0 FX @ 9317654 Arnold The study of natural hybridization between plant species is of fundamental importance for understanding the evolution of plants. This is due to the fact that an estimated 70% of all plant species have arisen through natural crosses between other species. Furthermore, almost all food and fiber crops used by humans reflect the result of natural or manmade crosses resulting in improved productivity and nutritive value. The studies outlined in this proposal will examine the effect of pollen tube growth rate, seed abortion and patterns of insect and bird pollinations on the success of natural crosses between the plant species Iris fulva , Iris hexagona , and Iris brevicaulis . These plants hybridize readily under artificial conditions and there are numerous natural hybrid populations formed by crosses between the species. Therefore, this species complex will allow a determination of what processes are important in limiting and promoting natural and experimental hybridization. Such an understanding should allow a better definition of how natural hybridization has come about in numerous plant species. In addition, data from these studies will be very applicable to plant breeders who need to know what mechanisms might restrict their attempts to cross agriculturally important species and thus limit the efficiency of crossing programs.
