Senin, 15 Juli 2013

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Secondary Growth And Development Processes Of Plant

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In addition to the elongation process, plants also grow bigger the increasing diameter of stem and root is called secondary growth. All gymnosperm and dicotyl undergo this process. On the other hands, only several monocotyl undergo secondary growth. For example Palmae.

Secondary growth occurs as a concequence of lateral meristematic cell activity. There are two types of lateral meristem, vascular cambium and cork cambium. Vascular cambium is sited between xylem and phloem.

Vascular cambium activity produces new cells. It produces secondary xylem to the inside and secondary phloem to the outside (see Figure)
Secondary Growrh is marked by the formation of new cell in the form of secondary xylem and secondary phloem


On stem, the xylem, which is known as wood, will get thicker, harder, and contain lignin. Xylem tissues produced in dry season have smaller and darker cells because of the limitation of water during dr5r season, while xylem tissues produced in wet season has relatively larger and brighter cells. Layers produced from woody tissue are called annual rings (see Figure )
The anatomy of stem's secondary growth


The activity of cork cambium produces cork tissue which is necessary for protection. Cork layers will replace dry and peeled off epidermal tissue. Cork layer, cork cambium, and secondary phloem will form bark. Phloem which is necessary to transport photosynthesis product is the youngest secondary phloem located behind cork cambium.

Secondary growth also occurs on root; it is conducted by the activity of vascular cambium. It produces secondary xylem inside and secondary phloem outside. Meanwhile, cork cambium forms cork tissue.

Part of root which is necessary to absorb water and mineral salt is young root. It is because cortex tissue and epidermis on mature root have been replaced by cork tissue which is difficulty emerged by water.
The anatomy of stem's secondary growth


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