Plants cannot run away from a predator, instead they have to defend themselves on the ground. Which of the following is NOT a way in which plants defend themselves from herbivores?
a. Harden their tissues with indigestible fiber such as lignin
b. Produce compounds that are toxic to herbivores
c. Release volatile compounds that attract the predators of herbivores
d. Physical defenses such as thorns
e. Produce flowers with higher nectar content
