Angiosperms are the most diversified group in the plant kingdom, consisting of around 2,00,000 species. This includes herbs, shrubs, and trees, all of which reproduce sexually through seeds. Depending on the number of cotyledons in the seed, angiosperms are of two types- monocot and dicot plants. The differences between the plants arising from a monocotyledonous seed and from a dicotyledonous seed are very evident. Let’s take a look at the anatomy of dicotyledonous and monocotyledonous plants.
Dicotyledonous and Monocotyledonous Roots
- Dicot plants have the taproot system.
- The outermost layer is called epidermis. The epidermal cells sometimes project out which appear as the root hairs.
- The epidermis is followed by multi-layered cortex, loosely made of the parenchyma cells with intercellular spaces.
- The inner layer of the cortex is called endodermis, which is tightly packed by the barrel shaped-cells.
- Endodermis is followed by pericycle, which are a few layers of thick-walled parenchyma cells.
- In dicots, the central pith is inconspicuous.
- The number of xylem and phloem are two to four.
- The xylem and phloem are distinguished by a layer of parenchymatous cells called conjunctive tissue.
During secondary growth, the cambium separates the xylem and phloem. Pericycle, vascular bundles and pith fuse to form stele in dicots.
Monocot roots do not show much difference in the anatomy from that of the dicot roots.
- Monocot plants have an adventitious root system.
- As in the dicots, the epidermis forms the outermost layer, followed by cortex, endodermis, pericycle, vascular bundles (xylem and phloem) and pith.
- Pith is large and conspicuous.
- The number of xylem in a monocot is six or more.
- Secondary growth is absent in the monocot plants.
Dicotyledonous and Monocotyledonous Stem
The dicotyledonous stem is usually solid. The transverse section of a typical young dicotyledonous stem consists of the following parts:
- The epidermis is the outermost protective layer which is covered with a thin layer of cuticle.
- Epidermis possesses trichomes and a few stomata.
- Cortex is multi-layered cells sandwiched between epidermis and pericycle.
- The outer layer, hypodermis (collenchymatous cells), the cortical layers (parenchymatous cells) and the inner layer, endodermis together make up the three subzones of the cortex.
- Next to endodermis is the pericycle which is constituted of semi-lunar patches of sclerenchyma.
- ‘Circled’/ ‘ring’ arrangement of vascular bundles is present only in dicot stem.
- The Vascular bundle is conjoint, open and with endarch protoxylem.
- Pith is evident and is made of parenchymatous cells.
Monocot stem is usually hollow with no secondary growth. The anatomy of monocot and dicot stem are similar, however, some notable differences are as follows:
- The hypodermis of the cortex in monocots is made of sclerenchymatous cells.
- Vascular bundles are numerous but scattered, conjoint and closed, surrounded by the ground tissue.
- Phloem parenchyma is absent.
Dicotyledonous and Monocotyledonous Leaves
Dicotyledonous leaf shows reticulate venation.
- Lamina consists of epidermis, mesophyll and vascular system.
- The epidermis is covered by cuticle and stomata; abaxial epidermis (lower surface) possesses more stomata than adaxial epidermis (upper surface). Sometimes adaxial epidermis lack stomata.
- Mesophyll, (parenchymatous cells) composed of the palisade and spongy parenchyma is present in between the adaxial epidermis and abaxial epidermis.
- The chloroplasts present in mesophyll perform photosynthesis in leaves.
- Vascular bundles are surrounded by bundle sheath cells and form the veins and midrib.
Monocotyledonous leaves are characterized by the parallel venation. The anatomy of a monocot leaf includes:
- Both adaxial epidermis and abaxial epidermis bear stomata.
- There is no differentiated palisade and spongy parenchyma of the mesophyll.
- Bulliform cells are present which is developed from adaxial epidermal cells and the veins.
- Bulliform cells are large, void cells which are responsible for the curling of leaves for minimal loss of water.
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