A certain cultivated herb is one of a group of closely related plants that thrive in soil with high concentrations of metals that are toxic to most other plants  Agronomists studying the herb have discovered that it produces large amounts of histidine, an amino acid that, in test-tube solutions, renders these metals chemically inert
Possibly, ttherefore, the herb' s high histidine production is what allows it to grow in metal-rich soils, a hypothesis that would gain support if
others of the closely related group of plants are also found to produce histidine in large quantities