Plants reveal many of the Earth's memories. Plants will "remember" when they've been attacked. They respond faster to future attacks by hastening production of chemical defenses. Plants defend themselves using a chemical pathway, called a signal-transduction pathway, that parallels the one involved when animals register damage or injury internally and respond to it. Long term learning, along with random mutations, account for evolution. Most trees contain rings that show how old they are.

People need to be reminded of the fragility of planet diversity, including the diversity of plant life. There are varieties of plants that are becoming extinct mainly because of human interactions. Two holidays dedicated to hindering this adverse affect are Arbor Day, a day to plant new trees, and Earth Day, a day to protect the environment. National parks were created not only to protect the environment, but also to remind us of the beauty of nature.