Monocotyledonous Root :
- Monocot root have similar tissues as in dicot except :-
- It contains more than six xylem bundles called polyarch.
- Pith is large and well developed.
- Do not undergo any secondary growth.
Dicotyledonous Stem :
- Outermost layer is epidermis.
- Epidermis covered with thin layer of cuticle and has trichomes and few stomata.
- The cells arranged in multiple layers in-between epidermis and pericycle constitute the cortex.
- Cortex has three sub-zones :
- Hypodermis: a few layers of collenchymatous cells below epidermis.
- Cortical layers: consists of rounded thin walled parenchymatous cells with intercellular spaces.
- Endodermis: it is the innermost layer of cortex. Cells are rich in starch grains and are referred to as starch sheath.
- Pericycle : present on the inner side of the endodermis and above the phloem in the form of semi-lunar patches of Sclerenchyma.
- Medullary rays: a few layers of radially placed parenchymatous cells present in between vascular bundles.
- A large number of vascular bundles arranged in a ring.
- Each vascular bundle is conjoint, open and endarch protoxylem.
- The central portion of stem constitutes the pith.
Monocotyledonous Stem :
- It has similar tissues with the dicot stem except in following-
- Sclerenchymatous hypodermis.
- Vascular bundles are scattered in the ground tissue.
- Each vascular bundle is covered by bundle sheath cells.
- Vascular bundles are conjoint and closed.
- Peripheral vascular bundles are smaller than central one.
- Phloem parenchyma is absent.
- Water containing cavities are present within the vascular bundles.
Dorsiventral (Dicotyledonous) Leaf :
- Vertical section of a Dorsiventral leaf shows three main parts:
- Epidermis.
- Mesophyll cells.
- Vascular systems.
- Epidermis covers both upper (adaxial) and lower (abaxial) surface of the leaf has a conspicuous cuticle.
- Abaxial surface has more stomata than the adaxial epidermis.
- Tissue between upper and lower epidermis called mesophyll.
- Mesophyll cells are two types:
- Palisade parenchyma
- Spongy parenchyma
- Adaxially placed palisade parenchyma is made up of elongated cells arranged vertically, parallel to each other.
- Spongy parenchyma: oval or round and loosely arranged cells below the palisade parenchyma.
- Vascular bundles are seen in the midrib and veins.
- The vascular bundles are surrounded by a layer of thick walled bundle sheath cells.
Isobilateral (Monocotyledonous) leaf :
- It is similar with Dorsiventral leaf in many respect except –
- Stomata are equally distributed on upper and lower epidermis.
- Mesophyll cells are not differentiated into palisade and spongy.
- In grasses, certain adaxial epidermal cells along the veins modified themselves into large, empty, colourless cells called bulliform cells.
- Causes rolling of leaves to reduce transpiration during water stress.
