Step 1: Understanding the Concept:
The concentration of active constituents in a plant varies throughout its growth cycle. Proper timing of collection is crucial to ensure maximum therapeutic potency.
Step 2: Detailed Explanation:
1. Digitalis (Foxglove): Digitalis purpurea is a biennial plant (lives for two years).
2. Timing: The highest concentration of cardioactive glycosides is found in the leaves collected during the second year of growth, specifically just as the plant begins to flower (flowering stage).
3. Drying: After collection, the leaves must be dried immediately at temperatures below 60 \(^\circ\)C to prevent the enzymatic hydrolysis of the glycosides.
Step 3: Final Answer:
The flowering stage represents the peak of metabolic activity and glycoside concentration in Digitalis leaves.