Tag: botany

Medullary ray is a band of parenchyma in the secondary xylem extending into the secondary phloem of the stems of certain vascular plants, formed by the cambium and helps for the storage of food and conduction of nutrients. it helps in the gaseous exchange through the intercellular spaces.

• The roots that arise horizontally from the primary roots which provide anchorage to the plants and fixes it into the soil. 
• These roots help in the uptake of water and nutrients from the soil which is required for the growth and development of the plants.
  
• They are endogenous in nature as it is developed from the cells of the pericycle which become meristematic and undergoes periclinal (parallel to the surface of a part) and anticlinal (right angles to the surface) division.
• So, the correct answer is 'Pericycle'.

• Passage cells are also known as transfusion cells.
• They are thin-walled cells which lack suberin and are found in the endodermis (is the central innermost layer of the cortex) of vascular plants (plants which consist of vascular tissues i.e, xylem and phloem).
• They are located opposite the protoxylem strands or elements.
• They are found in the endodermis of dicots.
• So, the correct answer is 'Protoxylem elements'.

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.