However, most of the monocots are herbaceous with weak cambium that cannot hold woody tissues. Their root system consists of various roots characterized by their growth and complexity. The adventitious roots develop from other regions of the seed than the radical. The lack of cambium in roots gets replaced by the adventitious roots that provide stability and strength to the plant.
What are Dicot Roots
Similarities between Monocot and Dicot Roots
What is the Difference between Monocot and Dicot Roots
Summary
Depending on the plant species, dicot roots can be both herbaceous and woody. The woody root system has cambium, which enables the growth of large plants with thick stems. Some dicot plants might have modified roots for different purposes like respiration, food storage, and mechanical support.
Structure
The anatomy or the internal structure of both monocot and dicot roots share the following parts when viewed under a microscope. a. Epiblema (Piliferous Layer or Epidermis):
Epiblema or epidermis is the outermost layer of roots, composed of a compact layer of thin-walled, polygonal parenchymatous cells with no intercellular spaces.Some of the epidermal cells of both monocot and dicot roots produce specialized root hairs present in the maturation zone.It is also called the piliferous layer due to the presence of hair cells. However, the intercellular spaces are absent.In monocots, the epidermis, alternatively known as rhizodermis, comprises hair-forming trichoblasts and non-root hair-forming atrichoblasts. Also, they possess a specialized multilayered epidermis called velamen, involved in gaseous exchange.The epiblema is short-lived, and in older roots, it gets replaced by a lignified, suberized exodermis.In dicot roots, the epidermis and other root tissues get removed and later replaced by cork cambium. On the other hand, in the monocot plant, the epidermis persists and forms a protective cuticle.In both types of roots, the epidermis protects the internal tissues. The minute root hairs help absorb water and minerals from the soil by providing a larger surface area.
b. Cortex:
It is the tissue present underneath the epidermis, composed of several layers of cortical cells.The cortical cells are thin-walled, multilayered, and parenchymatous in monocots and have sufficiently large intercellular spaces. On the contrary, the cortex of dicot roots consists of sclerenchyma and parenchyma.In some plants, the cortical cells of the outer layer undergo suberization and form a single or multilayered exodermis.The primary function of the cortex is the movement of water from the epidermis to the inner tissues. Also, the cells of this region store starch in the form of starch grains and contain leucoplasts.Compared to the dicots, monocots have a wider cortex, containing about eighteen layers of parenchymatous cells.
c. Endodermis:
It is another dermal layer, present between the cortex and the central vascular tissues of the root, acting as a barrier.The endodermis is composed of tightly packed, single-layered, barrel-shaped cells that lack any intercellular spaces.The young and immature cells of the endodermis have an internal band of suberin and lignin, giving rise to a layer of Casparian strip. As the cells mature, it becomes indistinguishable due to the thickening of the cells.In monocot plants, the internal layer of cells of the endodermis gives rise to the adventitious roots.The thickened or older endodermal cells help in the passage of fluid through plasmodesmata.The endodermis acts as a biological checkpoint by regulating fluid flow between the cortex and the vascular tissue.
d. Pericycle:
It is a single-layered structure present underneath the endodermis.In monocots, the pericycle comprises sclerenchymatous cells along with few parenchymatous ones. The immature cells of this layer are thin-walled but later become thick-walled due to the deposition of certain substances. Also, the pericycle can be either single-layered or multilayered.In dicot roots, the pericycle comprises a particular type of parenchyma called prosenchyma, characterized by the abundance of protoplasm.In dicots, the lateral roots are endogenous. They originate from a part of the pericycle present opposite to the protoxylem.Pericycle in dicot roots forms the vascular cambium. During secondary growth, the cork cambium is also formed in dicot plants. In contrast, the cambium is not formed in monocot roots.The pericycle is an essential part of the root tissue. It is involved in forming lateral roots and cambium and provides support to the vascular tissue present beneath it.
e. Vascular Bundles:
They form the innermost tissues of the plant root consisting of alternate xylem and phloem units. The number of vascular bundles varies in monocots and dicots.In dicots, the bundles are radial and exarch. The protoxylem lies towards the outside (pericycle), and the metaxylem lies towards the center (pith). Also, their number varies between two to six (diarch to hexarch).Like dicots, the vascular bundles of monocots are also radial and exarch, but the number is always greater than six.The vascular bundles are arranged as a ring around a central pith in both monocot and dicot roots. Also, due to the alternate arrangement of xylem and phloem, they are termed radial bundles.In monocot, the xylem is composed of oval vessels and xylem parenchyma. In contrast, in the dicots, the cells are polygonal and thick-walled.The phloem bundles in monocots lie closer to the pith and consist of sieve tubes, companion cells, and phloem parenchyma. In dicots, the phloem bundles remain close to the pericycle and consist of similar structures and cells. The phloem fibers are absent in both.In both types of the root, xylem tissue helps in the conduction of water, whereas the phloem bundles assist in the conduction and storage of food.
f. Conjunctive tissues:
They are masses of parenchymatous or sclerenchymatous cells present between the xylem and phloem bundles in the vascular tissue.Compared to the dicot root, the monocot roots possess more conjunctive tissue due to the larger number of vascular bundles.In the dicot root, the conjunctive tissues and the pericycle produces the vascular cambium during secondary growth. On the contrary, in monocot roots, no cambium formation occurs.Conjunctive tissues are involved in the storage of food and also provide mechanical support to the root.
g. Pith:
It is the central mass of tissues composed of thin-walled parenchymatous cells present in the root vascular system.In monocots, the pith is prominent, with many cells that are either rounded or polygonal.In dicots, the pith is less prominent or less developed or may be completely absent in some cases.The cells of the pith remain loosely attached with large intercellular spaces in between.Pith aids in food storage and also helps in the dispersal of air between the vascular bundles.
h. Passage Cells:
The younger cells of the endodermis that do not have deposits of suberin or lignin are called passage cells. These cells are also called transfusion cells.They are prominent in monocot roots but are absent in dicots.These cells are often present near the protoxylem and enable the radial flow of material through the root system.As the name suggests, passage cells help conduct water and other materials between the cortex and the vascular bundles.
Functions
Main Function The primary function of both monocot and dicot root is to support the plant by anchoring it to the ground. Also, they aid in the absorption of water and minerals dissolved in the soil. The vascular system in the root then translocates the water and mineral to other parts of the plant. Other Common Functions The following are some other functions of these roots:
The root of some plants like radish and carrots is modified to store many food particles in different tissues, such as conjunctive tissue, pith, and cortex.Plants growing in marshy areas have specialized roots, termed pneumatophores, that come out to the soil to obtain oxygen. These roots have tiny pores called pneumatophores which help in gaseous exchange.Many dicot roots exhibit a symbiotic relationship with microorganisms like fungi that play essential roles in nitrogen fixation.Also, the roots of some plants are involved in the propagation and dispersal of the plants.
Monocot root has fibrous roots. Moreover, it has got numerous xylem and phloem in an alternating manner. The vessels of the xylem are rounded or oval. Conjunctive tissue in a monocot root is generally sclerenchymatous, and sometimes it could be parenchymatous as well. Dicot root has taproots. Moreover, it has got xylem in the shape of ‘X’, surrounded by the phloem. In a dicot root, the number of xylem and phloem is constant. In the transverse section, vessels of the xylem are angular or polygonal in shape. Conjunctive tissue in a dicot root is parenchymatous, which forms vascular cambium.
