Definition: A hard, thorny or needle-like structure which occurs on various organisms. Animals such as porcupines and sea urchins grow spines as a self-defense mechanism
Definition: a plant that produces wood as its structural tissue. Wood is a structural cellular adaptation that allows woody plants to grow from above ground stems year after year, thus making some woody plants the largest and tallest terrestrial plants. Wood is usually primarily composed of xylem cells with cell walls made of cellulose and lignin
