Features of the Internal structure of stem of Tridax

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Tridax procumbers is a common di­cotyledon plant whose stems are taken for anatomical studies. The transverse section of this stem shows the follow­ing features:

Epidermis:

The outer boundary is more or less circular having a sin­gle layered epidermis. The epidermal cells are rectangular without chloro­phyll. A number of multicellular epi­dermal hairs are found in this layer. Cuticle is thin.

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Hypodermis:

It is the outer zone of cortex and lies below the epidermis. It consists of a few layers of collenchymatous cells with distinct thickened intercellular spaces.

General cortex:

It is inner to hy­podermis and consists of several layers of thin walled parenchymatous cells. The outer layers contain chlorophyll within the cells.

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Endodermis:

It is the inner layer of cortex and consists of only one layer of barrel shaped cells. This layer possesses abundant starch and hence, called starch sheath.

Pericycle:

It is the outer layer of stele. It is sclerenchymatous in na­ture and continuous. How­ever, there are more layers of sclerenchyma opposite to vascular bundles.

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Vascular Bundles:

Several vascular bundles are arranged in one ring and very close to the pericycle. Each vascular bundle is a conjoint, col­lateral and open type with few layers of cambium in between xylem and phloem patches. The phloem is outer and xylem is inner in position. Xylem is endarch in nature. Xylem contains all vessels, tracheids, parenchyma and fibres. Protoxylem elements are smaller than metaxylem el­ements.

Pith (Medulla) The centre of the stem is occu­pied by a well developed parenchymatous pith. Pith is broad and has intercellu­lar spaces.

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