Tag: tissue systems

The tissues present in a plant which are dermal nor vascular are called ground tissues.

• The ground tissues consist of the following:-

Cortex is the ground tissue present between epidermis and endodermis. It is mostly composed of parenchymatous cells. Parenchymatous cells are thin walled polyhedral, isodiametric living cells with sufficient cytoplasm, one or more nuclei and nucleolus. They serve to store food. Chlorophyll is present in chlorenchyma which are specialized to perform photosynthesis and are present in leaves. Thus, the correct answer is option A.

Passage cells forms the endodermis of older roots of monocots. They are thin walled and have casparian strips, unlike the other cells that becomes suberized and waterproof. Passage cells function to allow transfer of solutes into the stele, in order to eventually reach the transpiration system.

Pericycle is a primary tissue of plant roots and is the site for the initiation of lateral roots and two secondary meristems, the vascular cambium and cork cambium (phellogen). 

The layers of cells lying between endodermis and vascular bundle is pericycle. The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants. Although it is composed of non-vascular parenchyma cells, it is still considered part of the vascular cylinder, because it arises from the procambium as do the vascular tissues it surrounds.

Heartwood is also called as 'duramen'. It is dead, central wood of trees. Its cells usually contain tannins or other substances that make it dark in colour and sometimes aromatic. Heartwood is mechanically strong, resistant to decay and less easily penetrated by wood-preservative chemicals than other types of wood.

Passage cells are endodermal cells of older roots which have retained thin walls and Casparian strips rather than becoming suberized and waterproof like the other cells around them, to continue to allow some symplastic flow to the inside (cortex to pericycle). 

Casparian strip is a band of cell wall material deposited on the radial and transverse walls of the endodermis and is chemically different from the rest of the cell wall. The cell wall being made of lignin and without suberin, whereas the Casparian strip is made of suberin and sometimes lignin. It blocks the passive flow of materials, such as water and solutes into the stele of a plant.

The endodermis is the central, innermost layer of cortex in some land plants. It is made of compact living cells surrounded by an outer ring of endodermal cells that are impregnated with hydrophobic substances (Casparian strip) to restrict apoplastic flow of water to the inside. The endodermis is the boundary between the cortex and the stele.