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Types of Meristems

 

Lateral meristems. If apical meristems—and primary growth—were the only means by which a plant grew in size, however, we'd have very skinny trees! But of course in addition to lengthening, some roots and shoots eventually also increase in girth and become woody. This is termed secondary growth, and it takes place in lateral meristems. There are two types of lateral meristems in woody plants; both are found in cylinder-shaped regions below the bark.

Tree Cross-Section

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The vascular cambium lies between the wood and the inner bark. During secondary growth, new xylem cells formed by the vascular cambium become thick-walled and sturdy, and the living contents die. As the branch or trunk enlarges in circumference, these cells make up the bulk of the stem tissue, forming the secondary xylem, or what we commonly call wood. Thinner-walled phloem cells divide outward, surrounding the wood; this forms the inner bark.

The cork cambium lies closer to the surface, and produces the outer bark.

If you take a freshly-cut branch or log and peel away the bark right down to the wood, you’ll feel a moist, slippery surface on both the wood and the inner bark. This is the region of the vascular cambium. Never peel the bark off a living plant!

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The inner bark consists of living cells.
The outer bark is made up of dead cells.
Cork is a secondary tissue that replaces the epidermis in woody stems.

 

meristems continued


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