You’ve probably noticed that the stems of many plants are green and smooth. But what about the stems of woody plants? For example, why are tree trunks brown, bumpy, and hard? This is because the trunk, branches, and roots of a tree are covered with bark! Tree bark is the outer tissue of the tree.
Did you know there are two kinds of tree bark?! The inner bark is soft bark that helps transport food from the leaves to the rest of the tree. It is made of tissue called phloem. When phloem dies, it becomes part of the outer bark. The outer bark, also known as rhytidome, is made mostly of dead tissue.
Why do trees need bark? For one thing, bark is like armor for trees and protects them from damage by creatures, and from organisms that can make the tree sick. Bark also protects trees from severe heat and cold, as well as from harsh sunlight. Bark even helps prevent water loss from the tree!