Physical defenses Hooks, spines (cactus) Dense trichomes (leaf hairs) Magnolia Overall leaf toughness such as the leaves in an oak tree. Leaf toughness tends to increase as the summer season progresses.
Chemical defenses Systemic chemical defenses are present is some effective levels in the plant at all times. Example is salicylic acid in willow trees, tannic acid in oaks
Induced chemical defenses may by synthesized upon attack by herbivores. Let’s look at figure 39.22 on page 771.