Based on the number of cotyledons, all vascular plants are classified into dicots and monocots. Most monocotyledons are angiosperms and the seed contains one embryonic leaf. Some examples are ginger, onions, and wheat. Dicotyledons have two embryonic leaves on the seed. Some examples are pea, lentils, beans, etc.
The root system of both these types of plants has unique, distinguishable characteristics. We will study them in this article.
A monocot root shows 5 distinct regions. We will discuss each of them in the following. These parts are:
Epiblema: This is the single outermost layer of the root made entirely from parenchymatous cells and does not have any intercellular space. It bears unicellular epidermal root hairs with less cutin and more cuticles. This region of the monocot root is also known as rhizodermis.
Cortex: It is made up of multi-layered oval parenchymatous cells and has intercellular spaces. These spaces help in gas exchange and storage of starch. In monocots, few layers of cortex below the epiblema give rise to a layer called exodermis which is made from multi-layered cuticularised sclerenchyma cells.
Endodermis: It is the innermost layer of cortex made of barrel-shaped parenchyma. It shows a ring-like formation around the stele and the cells are characterized by Casparian stripes. Due to the presence of Casparian stripes, endodermis forms a water-tight jacket around the vascular tissue, therefore it is also called a biological barrier. Endodermis regulates both inward and outward flow of water and minerals and prevents the diffusion of air into xylem elements.
Pericycle: It is made from thin-walled parenchymatous cells and is the outermost layer of the stellar system. The cells can become sclerenchymatous in older roots. Numerous lateral roots arise from this layer.
Vascular Bundle: The xylem and phloem systems are found in different radii alternating with each other in this region. The numbers of these systems vary from 8-46. The protoxylem lies towards the periphery whilst the metaxylem lies towards the center. The protoxylem has spiral thickening and the metaxylem has pitted thickening. The phloem consists of sieve tubes, phloem parenchyma, and companion cells. The region functions as a transportation system of elements within the plant body.
Conjunctive Tissue: It is made of parenchymatous tissue and separates the xylem and phloem system.
Pith: It is a large well-developed part of the monocot root and is made up of thinly walled parenchymatous tissue. It contains high amounts of starch grains.
The following are the distinguishing features of the dicot root system. The five distinct regions are as same as the monocot root system
Epiblema: It is uniseriate, colorless, thin-walled, and without intercellular spaces. The epiblema produces unicellular root hairs. Stomata and cuticle are absent.
Cortex: It is thin-walled and made from polygonal or circular parenchymatous cells that usually have intercellular spaces. It is responsible for the transportation of salts and water from root hairs to the center of the root.
Endodermis: It is made of barrel-shaped compact parenchymatous cells and gas both passage cells and Casparian stripes. This region allows the radial diffusion of water and minerals through the endodermis.
Pericycle: It is composed of a uniseriate layer of parenchymatous cells without intercellular spaces. Lateral meristem and lateral roots grow from the Pericycle region.
Vascular Region: The bundles are radial. The xylem system consists of tracheids, vessels, xylem fibres and xylem parenchyma. The phloem system consists of sieve tubes, phloem parenchyma and companion cells, Phloem fibres are absent or reduced.
Pith: It is centrally located and is very small and is made of polygonal parenchymatous cells. It functions as a storage unit of food.
The differences between dicot root and monocot root are narrated below:
1. What type of root system is found in monocot and dicot plants?
A: Monocot plants have a fibrous root system. This type of root system is located near the soil surface, and it forms a dense network of roots that also helps the prevention of soil erosion. Some plants have both tap roots and fibrous roots.
Dicot plants show a tap root system and it grows down vertically. The root system penetrates deep into the soil and many small lateral roots arise from this type of root.
2. Is pith present in monocot roots?
A: There is no pith region in monocot roots. Even if the pith region is present it would be in a reduced state. It is formed of polygonal parenchymatous cells and acts as a food storage unit.
3. What is the piliferous layer?
A: The single-layered,thin-walled, colourless polygonal parenchymatous outer layer of the monocot root is called the piliferous layer. It is also called the epiblema of the monocot root.