surrounded by few layer of sclerenchyma cells called bundle sheath . (a) Xylem: It consists of metaxylem and protoxylem. Xylem vessels are arranged in V or Y shape. In mature vascular bundle, the lower most protoxylem disintegrates and form a cavity.
This is called protoxylem lacuna. (b) Phloem: It consists of sieve tube elements and companion cells. Phloem parenchyma, and phloem fibers are absent. .
Pith: Pith is not differentiated in monocot stems. Table . Differences between Dicot Stem Ex.Sunflower and Monocot Stem Ex.Maize S. No.
Tissues Dicot Stem Monocot Stem Hypodermis Collenchymatous Sclerenchymatous Ground tissue Differentiated into cortex, endodermis, pericycle and pith Undifferentiated Vascular bundles (i) Less in number (ii) Uniform in size (iii) Arranged in a ring (iv) Open (Cambium present) (v) Bundle sheath absent (i) Numerous (ii) Smaller near periphery, bigger in the centre (iii) Scattered (iv) Closed (Cambium absent) (v) Bundle sheath present Secondary growth Present Mostly absent Pith Present Absent Medullary rays Present Absent . Internal Structure of Dicot Leaf (Dorsiventral Leaf) Ex. Mango Leaf The transverse section of leaf shows the following structures. A sector enlarged Ground plan Vascular bundles Vascular bundles Bundle sheath Protoxylem Metaxylem Phloem Chlorenchyma Hypodermis Epidermis Cuticle Ground tissue Ground tissue Epidermis Figure .
Transverse section of Monocot stem (i) Upper epidermis: This is the outermost layer made of single layered parenchymatous cells without intercellular spaces. The outer wall of the cells are cuticularized. Stomata are less in number. Plant Anatomy and Plant Physiology (ii) Lower epidermis: It is a single layer of parenchymatous cells with a thin cuticle.
It contains numerous stomata. Chloroplasts are present only in guard cells. The lower epidermis helps in the exchange of gases. The loss of water vapour is facilitated through this chamber.
(iii) Mesophyll: The tissue present between the upper and lower epidermis is called mesophyll. It is differentiated into Palisade parenchyma and Spongy parenchyma. a) Palisade parenchyma: It is found just below the upper epidermis. The cells are elongated.
These cells have more number of chloroplasts. The cells do not