GROWTH AND DEVELOPMENT OF ORGANIC ARSENICAL-SUSCEPTIBLE AND ARSENICAL-RESISTANT COMMON COCKLEBUR (XANTHIUM-STRUMARIUM) BIOTYPES UNDER NONCOMPETITIVE CONDITIONS

The growth, development, and reproductive potential of several populat ions of organic arsenical-susceptible (S) and -resistant (R) common co cklebur biotypes were compared under noncompetitive field conditions. Plant height, leaf area, aboveground dry weights, and relative growth rate (RGR) were measured periodically during the growing season. Days to flowering, bur dry weight, and number of burs per plant were also r ecorded. Arsenical S- and R-biotypes were similar in all measured para meters of growth, development, and reproductive potential. Populations within each biotype varied occasionally in plant height, leaf area, a boveground dry weights, and reproductive potential.