Anatomy Of Flowering Plants

In bicollateral vascular bundles, phloem patches remain on both sides of the xylem, The phloem present on the outer side of xylem as in collateral vascular bundle is called outer or external phloem. Phloem present on the inner side of xylem is called inner or internal phloem. This type of vascular bundle occurs mainly in the Family Cucurbitaceae. It also occurs in some members of Solanaceae, Convolvulaceae etc. These bundles are always open as the outer and inner patches of phloem are separated from the central xylem by two strips of cambium. Pumpkin (Cucurbita maxima) belongs to Cucurbitaceae family and has bicollateral vascular bundle in its stem.

Sclereids not sdlerenchyma fibres form stony endocarp of many fruits called stone fruits, e.g., almond, coconut. Sclereids. may occur singly or in groups. They provide stiffness to the part in which they occur. The important types of sclereids are stone cells or brachysclereids, macrosclereids, osteosclereids, astrosclereids, filiform selereids and trichosclereids. Brachysclereids are unbranched, short and isodiametric with rarniform (branched) pits and are responsible for grittiness of guava) sapota, apple and pea. Macrosclereids are present in seed coat of pulses (legume). They are slightly elongated and columnar or rod shaped cells and form palisade like layer in seed coat.

Sclereids. may occur singly or in groups. They provide stiffness to the part in which they occur. The important types of sclereids are stone cells or brachysclereids, macrosclereids, osteosclereids, astrosclereids, filiform selereids and trichosclereids. Brachysclereids are unbranched, short and isodiametric with rarniform (branched) pits and are responsible for grittiness of guava) sapota, apple and pea. Macrosclereids are present in seed coat of pulses (legume). They are slightly elongated and columnar or rod shaped cells and form palisade like layer in seed coat.

Xylem and phloem are complex vascular tissues in plants. Xylem functions as a conducting tissue for water and minerals from roots to the stem and leaves. It is composed of four different kinds of elements, namely, tracheids, vessels, xylem fibres and xylem parenchyma in angiosperms. Gymnosperms lack vessels in their xylem. Phloem transports food materials, usually from leaves to other parts of the plant. It is composed of sieve tube elements, companion cells, phloem parenchyma and phloem fibres in angiosperms. Gymnosperms lack sieve tubes and companion cells.

Sclerenchyma is a simple supportive tissue of highly thick-walled cells with little or no protoplasm. It is generally dead.

Meristem is a plant tissue consisting of actively dividing cells that give rise to new cells that differentiate into new tissues of the plant. The most important meristem that occur at the tips of shoot and root is called apical meristem. So, active cell division takes place at the tips of roots and stems of plant.