Page 89 - Biology Form Two

Biology for Secondary Schools

Vascular bundles in leaves
Both the monocot and dicot leaves have vascular bundles surrounded by a
bundle sheath. The bundle sheath has one or more layers of ground tissue called
parenchyma cells. The main function of the bundle sheath is to protect the leaf
veins.
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Monocotyledonous leaves
In monocot leaves, vascular bundles form parallel veins. The phloem tissue is
located towards the lower epidermis of the leaf while the xylem tissue is located
towards the upper epidermis, as shown in Figure 4.10.
Cuticle

Upper epidermis
Xylem

Bundle sheath

Phloem
Lower epidermis

Cuticle
Stomata

Figure 4.10: Cross-section of a monocot leaf
Dicotyledonous leaves
In the dicot leaf, vascular bundles form net-like veins. Like in the monocot leaf,
the xylem tissue in a dicot leaf is located towards the upper epidermis of the leaf.
The phloem tissue is located towards the lower epidermis of the leaf, as shown
in Figure 4.11.
Cuticle

Upper epidermis

Bundle sheath

Xylem

Cambium

Phloem
Lower epidermis

Cuticle

Figure 4.11: Cross-section of a dicot leaf

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