Secondary Growth: Annual Rings

Also called

secondary growth · annual rings · growth rings · vascular cambium · cork cambium · phellogen · secondary xylem · secondary phloem · spring wood · autumn wood · heartwood · sapwood · bark · dicot stem · dendrochronology · द्वितीयक वृद्धि · वार्षिक वलय · अंतःकाष्ठ

Topics

• A young dicot stem has a ring of open vascular bundles: xylem inside, phloem outside, cambium between them.
• Cambium between the bundles (interfascicular) joins the cambium inside them to make a complete ring.
• The cambium cuts off secondary xylem (wood) inward and secondary phloem outward; it makes more xylem.
• In spring the cambium is very active: wide, pale spring wood with large vessels; in autumn, narrow dark wood.
• One band of spring wood and one of autumn wood make an annual ring; counting the rings gives the tree’s age.
• Old central wood stops conducting and fills with tannins and resins: dark, hard heartwood.
• The outer, lighter sapwood still carries water and minerals up from the root.
• A cork cambium (phellogen) in the cortex makes cork outward; bark is every tissue outside the vascular cambium.

About this model

A GLB file of about 955 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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