leaf age in a sentence

1. Her M . A . and doctorate were completed at the University of Chicago by studying resource availability theory, including the effects of leaf age and plant life history patterns on herbivory, and patterns of plant defenses.
2. In studies of " T . pachysiphon ", it was found that alkaloid content including that of apparicine was greatest in young leaves and leaves receiving greater shade, and varied with leaf age, plant age, and provenance.
3. It's difficult to find leaf age in a sentence.