Rabu, 10 Oktober 2012

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Structure Of Plant Organ Stem

Structure Of Plant Organ Stem

Dicotyledon Stem 

Dicotyledon stem grows from apical meristem which makes the stem always elongate. The part of the apical meristem is called growth point. The tissues that compose dicotyledon stem, from the epidermis inward are: epidermis, cortex, endodermis, pith, cambium, phloem, xylem, and pith rays.

Xylem and phoem on dicotyledon stem form vascular bundle. Each vascular bundle is arranged on the same radii.The outer layer of vascular bundle is phloem, whereares the inner layer is xylem. The type vascular bundle with xylem and phloem arrangement on the same radii. Is called collateral. If cambium presents in between phloem and xylem, it is called open collateral, but there is no cambium, it is called closed collateral. Dicotyledon has collateral open vascular bundle. 

Cambium development on dicotyledon stem gives rise to xylem formation toward the interior and phloem toward the exterior of the stem. Based on the location, there are two types of cambium as follows. 

  1. Fascicular cambium, which is located between vascular bundle and parenchyma (pith). 
  2. Interfascicular cambium, which is located between two vascular bundles. 

In dicotyledon stem secondary growth (secondary ring) occurs causing the stem to increase in girth as a result from cambium growth. The cambium tissue is called secondary growth point

Cambium activity give rise to the formation of annual rings, the rings that indicate the division activity of cambium. 

Monocotyledom Stem 

Monocotyledon stem has small apical meristem and consists of epidermis, ground meristem, and vascular bundle. 

Monocotyledon has scattered vascular bundle on the ground meristem and closed collateral type. Each vascular bundle is surrounded by bundle sheath (sclerenchyma bundle) which is usually thick, particularly on the sheath edge. 

On some monocotyledon that has tree form, parenchyma sheath presents outside the vascular bundle distribution. Cambium can be found in this region, which gives rise to the secondary growth of the plant.

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