Monocot and Dicot Stem
3 Minutes
Differences between monocot and dicot stems for students, explaining cortex layers and vascular bundle arrangement. An English science lesson.
- Epidermis, cuticle, and cortex cell layers in both stem types
- Vascular bundles, cambium, and secondary growth in stems
- Why dicot stems have a central pith while monocot stems do not
What this lesson teaches
Monocot and dicot stems are the supporting parts of plants that show clear differences under a microscope. They differ in the structure of their cortex layers, the arrangement and type of their vascular bundles, and their ability to undergo secondary growth.
Outer layers and cortex structure
- The outermost tissue layer of the stem is the epidermis, which is protected by an outer cuticle layer.
- Below the epidermis is the cortex, which forms the tissue layers beneath the surface.
- In a monocot stem, the cortex is a single layer called the hypodermis, made of sclerenchyma cells with scattered chlorenchyma cells that make some stems look green.
- In a dicot stem, the cortex is divided into three distinct layers: an outer hypodermis of collenchyma cells, a middle cortex of chlorenchyma cells, and an inner cortex of parenchyma cells.
Vascular bundle arrangement and pith
- Monocot stems contain a larger number of vascular bundles arranged here and there in a scattered, random manner.
- Dicot stems contain fewer vascular bundles that are organized neatly in a ring shape.
- Because dicot vascular bundles form a ring, a distinct central region called the pith is present in the middle of the stem.
- Monocot stems do not have a pith because their vascular bundles are scattered randomly throughout the tissue.
Open and closed collateral bundles
In monocot plants, there is no cambium layer to separate the xylem and phloem within the vascular bundle. For this reason, the vascular bundle in a monocot is described as a closed collateral bundle. In dicot plants, a layer called cambium separates the xylem and phloem from each other. Because this cambium layer is present, the vascular bundle in a dicot is described as an open collateral bundle.
Cambium and secondary growth
Secondary growth refers to the stem growth that occurs because of cambium cells. Since cambium is present inside dicot stems, secondary growth takes place only in dicot plants. Monocot stems do not possess cambium within their vascular bundles, so secondary growth does not happen in monocots.