The term “tree juice” is a common, though unscientific, umbrella phrase used to describe the diverse fluids that move through a tree. These natural secretions—sap, resin, and gums—are fundamental to a tree’s survival, each serving a distinct biological purpose. Sap acts as the tree’s internal circulatory system, while resin and gums are specialized compounds secreted for defense and wound repair.
Sap: The Tree’s Internal Transport System
Sap is the watery fluid that moves through the vascular tissues of a tree, functioning as the primary transport medium for nutrients and water. This fluid travels through two distinct systems: the xylem and the phloem. Xylem sap, consisting mainly of water, dissolved minerals, and hormones, is drawn upward from the roots toward the leaves, carrying the raw materials needed for growth and photosynthesis.
Phloem sap is notably richer in organic compounds like sugars, primarily sucrose, produced during photosynthesis in the leaves. Phloem distributes this food energy, along with hormones and mineral elements, to all other parts of the tree, including the roots, buds, and fruits, which are known as “sinks.” This flow within the phloem is bidirectional, moving from areas of sugar production to areas of storage or growth.
Resin and Gums: The Tree’s Natural Defenses
In contrast to sap, resins and gums are external secretions produced for protection. These substances are stored in specialized ducts and cavities, not the tree’s main vascular transport system. Resin is a highly viscous, water-insoluble mixture of organic compounds, predominantly complex chemicals called terpenes.
When a tree is wounded, it secretes resin to seal the injury site. This sticky substance hardens upon exposure to air, forming a physical barrier that prevents water loss and stops pathogens like fungi and bacteria from entering. The chemical components of the resin also repel wood-boring insects, acting as the tree’s natural antiseptic and bandage.
Gums are mainly water-soluble polysaccharides that fulfill a similar protective function. When a tree is stressed or injured, cells may break down in a process called gummosis, leading to the exudation of a sticky gum that swells with water to quickly plug the wound. Resins are based on terpenes and are not water-soluble, while gums are sugar-based and are water-soluble. Both are effective, localized defense mechanisms.
Practical Applications and Common Examples
The properties of these tree secretions have been utilized by humans for centuries. The most common example of using sap is the production of maple syrup, where the xylem sap of sugar maple trees is collected and boiled to concentrate its sucrose content. Other trees, like birch, also yield a watery sap that is sometimes tapped for consumption.
Resins and gums offer a wide range of industrial and cultural applications due to their adhesive and aromatic qualities. Pine pitch, a type of resin, has historically been used as a sealant for boats and in varnishes and adhesives. Highly aromatic resins like frankincense and myrrh have been prized for millennia for use in incense and perfumes. Latex, a specialized fluid, is the source of natural rubber. Various tree gums, such as gum arabic, are used today as thickeners and emulsifiers in food, cosmetics, and printing ink.