Ground Tissue System in Monocot , Dicot Roots and Stems - Practice Questions & MCQ

Ground Tissue System

• The ground tissue system is present between the epidermal tissue system and the vascular tissue system.
• It is heterogeneous in nature because the tissues are involved in performing varied functions such as storage, excretion, secretion, etc.
• It forms the major part of the plant body. 
• It originates from the periblem and plerome of the apical meristem.
• The tissues of this system are made up of parenchyma, collenchyma, sclerenchyma. 
• It includes cortex, pericycle, pith, and rays.
• The following diagram shows an orientation of tissue systems in the primary dicot stem.

Components of Ground Tissue System - Cortex

Cortex:

• It is the extra stellar zone, that is, present outside the stele. 
• The region between the epidermis and stele is called the cortex.
• It consists of the following regions:

1. Hypodermis
2. General Cortex
3. Endodermis

1. Hypodermis

• It is present just below the epidermis.
• In the dicot stem, it is collenchymatous.
• In the monocot stem, it is sclerenchymatous.
• It is absent in roots.
• In the green stem of monocots, it can be chlorenchymatous, like, asparagus
• It provides protection to the underlying cortical tissues.
• It provides mechanical support to the peripheral region.

2. General Cortex

• It is located between hypodermis and endodermis. 
• It is largely parenchymatous.
• The cells are loosely arranged with intercellular spaces.
• The cells contain starch grains.
• Their cells may or may not have chloroplasts.
• Their function is to store the food and perform metabolic activities.

3. Endodermis or Starch sheath

• It is the innermost layer of the cortex.
• It is single-layered.
• The endodermal cells are compactly arranged.
• The endodermal cells are vertically elongated and appear barrel-shaped in cross-section. 
• The endodermal cells are characterized by the presence of suberin in the form of bands or strips that are called Casparian strips.
• Lignin may also be present in the Casparian strips.
• The endodermal cells that lack Casparian strips are called passage cells. These are present just opposite to the protoxylem.
• Endodermis is absent in the woody stem of dicot angiosperms and gymnosperms. 
• Endodermis is absent in angiosperm leaves.
• Endodermis behaves as a water-tight dam to check the loss of water and an air dam to check the entry of air in xylem elements. 

TIP:

• The cortex is homogenous in roots as the hypodermis is absent.
• The term ‘ground tissue’ is used to refer to undifferentiated general cortex and hypodermis.
   

Components of Ground Tissue System - Pericycle, Pith and Pith Rays

Pericycle:

• It is present between the endodermis and vascular bundles.
• It can be one or several layered.
• It is the outermost layer of the stele.
• Hence, it is an interstellar tissue.
• In all roots, it is homogeneous and parenchymatous.
• In dicot stem, it is heterogeneous and can be parenchymatous and sclerenchymatous.
• In monocots, it is sclerenchymatous.
• It is absent in the roots and stems of aquatic and parasitic plants.
• In pteridophytes, it is single-layered. 
• In gymnosperms, it is multi-layered.
• In angiosperms, it is 2 - 3 layered. 
• Pericycle gives rise to secondary meristem during secondary growth.
• In roots, it gives rise to lateral roots. It is called pericambium in this condition.
• The lateral roots are therefore known to have an endogenous origin.

TIP: All tissues on the inner side of the endodermis such as pericycle, vascular bundles, and pith constitute the stele.

Pith or Medulla:

• It is the internal ground tissue.
• It forms the central cylindrical core of the stem. 
• It is bounded by the vascular bundles externally.
• It is made up of loosely arranged parenchymatous cells.
• It may be chlorenchymatous in the young delicate stem.
• It is well developed in dicot stem.
• It is reduced in the dicot root.
• It is absent in the monocot stem.
• It is well developed in monocot root.
• In cucurbits, the pith is hollow.
• It stores food.

Pith Rays or Medullary Rays:

• The medullary rays are the long strips of parenchymatous cells passing in between two vascular bundles. 
• These are extensions of the pith cells.
• These are not so distinct in the roots.
• These help in the radial conduction of food and water.