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Roots, Tree - There are two basic types of tree roots: Woody and non-woody. Woody roots are organs that mechanically support the tree, store energy reserves, and transport liquids that contain many types of soluble substances. Woody roots have lignin along with cellulose and hemicelluloses in their cell walls. Woody roots have an outer bark and contains suberin. Suberin gives bark a corky characteristic. Suberin "waterproofs" the tissues. Woody roots usually grow outward and downward. New woody root tissues begin to grow soon after woody growth starts in the trunk. Non-woody roots are organs that absorb water and elements essential for growth. Further, there are two types of structures that form on non-woody roots: root hairs and mycorrhizae. Root hairs are organs that are extensions of epidermal cells. Mycorrhizae are organs composed of tree and fungus tissue, a composite structure. Non-woody roots have very little lignin in cell walls. Non-woody roots live for a short time; from a few weeks to a year. Some mycorrhizae "regrow" on themselves and may from for more than a year. Root hairs come fast and go fast. As conditions occur that support their growth, they grow. Root hairs are most common on young plants and plants growing in containers. Root hairs are not so common on most mature trees, especially forest trees. See "mycorrhizae" and "root hairs".
In other words. Roots are tree organs that: absorb liquids, provide mechanical support, manufacture growth chemicals, and store energy. Roots may be woody or nonwoody, short lived or long lived. There are many types of roots: Most common are prop, deep, shallow, pioneer, mycorrhizal, nodule, hair, and tap. Prop roots and other adventitious – type roots, grow from meristematic points. Prop roots grow downward from branches. Deep roots grow in loose sandy soils usually, and shallow roots grow in heavy soils mostly. Pioneer roots are destined to become woody roots from the moment they start to grow. Mycorrhizae are organs of tree and fungus tissues. Nodules are organs of micros, mostly bacteria, actinorhizae, or cyanobacteria, and tree tissues. Hair roots are single cells. Tap roots grow downward. There are many variations on the theme.
In other words. Roots are organs. Roots are organs. There are many sub-types of organs. They are absorb liquids, provide mechanical support, manufacture all types of chemicals required for the life of the tree, and they store energy. Roots may be woody. That means they have a lot of lignin or nonwoody which means they have a very little lignin. They may live for a very short time or they may live for a very long time. They may be shallow or they may be deep. You cannot put them all into one box. You could have adventitious, you could have prop roots, you can have meristematic points in roots. Roots do not regenerate. Usually you will find shallow roots in sort of heavy soils. You may find deep roots in the more loose type soil. That doesn’t hold true all the time because some trees have both shallow roots and deep roots. We keep thinking about the Jarah tree in Australia that has a shallow root system yet also has what is called sinker roots that go very deep. There are so many variations on the theme of roots. We have so many different types of organs – fungi, bacteria, actinorhizae, cyanobacteria and we don’t know how many other kinds of microorganisms are associated with the tree tissues to form a special kind of tissue with roots.