Platystemon californicus is a self-compatible, perfect-flowered, wind-pollinated annual plant exhibiting strict modular architecture (solitary flower per node) and extreme variability in numbers of stamens and carpels within flowers. Theory predicts that wind-pollinated species should allocate an increasing proportion of resources to male function as plants become larger. I found that larger plants produced more massive flowers (300-400% increase) and invested proportionally more resources (estimated as biomass) in stamens than in carpels than did flowers of smaller plants. Carpels represented less than 20% of the biomass contained in stamens at anthesis. Total flower biomass at anthesis and allocation to stamens vs. carpels also change at successively formed nodes. The first flower on a plant (the only flower produced by the smallest plants) produced fewer stamens and carpels and had a lower ratio of stamens to carpels than did subsequently produced flowers. Allocation shifts without a change in architecture suggest that changes in resource availability occur at successive nodes as plants grow larger. If resource availability influences allocation patterns within flowers and if carbon is a limiting resource, then carbon distribution patterns among nodes or carbon fixation rates at independent nodes must change during plant development. Such changes have been found in crop plants, but many models of resource allocation ignore demand-driven changes in carbon transport or photosynthetic rate and assume a constant resource pool.

Key words: architecture, Papaveraceae, Platystemon, reproduction, resource allocation, sex allocation