2011 American Scientists - Forever stamp

The 2011 USPS American Scientists series honors four brilliant minds who transformed our understanding of the natural world:

• Melvin Calvin — Chemist, Nobel Prize winner who discovered the Calvin cycle of photosynthesis
• Asa Gray — Botanist, America's foremost 19th-century botanist and champion of Darwin's theory of evolution
• Maria Goeppert Mayer — Physicist, Nobel Prize winner who developed the nuclear shell model
• Severo Ochoa — Biochemist, Nobel Prize winner who first synthesized RNA

A distinguished collectible for science enthusiasts, history lovers, and stamp collectors alike.