Minggu, 14 Juli 2013

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Primary Growth And Development Processes On Plant

Growth on plant occurs due to the activity of meristematic cells. meristematic cells are cells that actively divide themselves through mitosis. It is can be found mostly at the tips of roots or stems (bud) called apical meristem.

Apical meristematic cells countinuously divide as long as the plants are alive. The activity of apical meristem drives the elongation of root and stem. The process of meristematic cell division which is responsible for the increasing in length or height is called primary growth.

Meristematic cell activity on root enables root to grow downward into the deeper soil layer. On the tip of the root there is a calyptra whose function is to protect root while anchoring into the soil.
Primary Growth On Onion Root

figure shows the cross section of onion root having primary growth. root can be distinguished into three zones (areas), zone of division, zone of elongation, and zone of differentiation.

Cell division zone is composed of root apical meristem and its derivative cells. New cells and root cap are produced from this zone.

In elongation zone, cell extention occurs by which the Length can be ten times longer than its intial length. The cells Are responsible for forcing the tip of the cell into the soil.

In differentiation zone, there are three tissue systems of mature plant, namely dermal tissue, primary tissue, and vascular tissue. Dermal tissue (epidermis) is produced by protoderm which is the outermost layer of meristem.

Primary tissue is the innermost layer of apical meristem. It Will differentiate into cortex and pith. Cortex is located between stele and epidermis. The innermost layer of cortex is bounded by a layer of cell called endodermis.

Vascular tissue (stele) is a transportation tissue that consists of primary Xylem and primary phloem. It is produced by procambium which is located between protoderm and primary meristematic tissue.

Primary Growth On Stem bud

in Figure you can see primary growth on stem. There are two kinds of plant buds, terminal bud and. Axillary bud. Terminal bud bounded by primordial and located on the tip Of shoot that enables it to grow upward. Axillary bud (lateral but) is located on the leaf internode which will form branch or flower.

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