Anatomy of Flowering Plants — Class 11 Biology

This chapter examines the internal structure of angiosperms, organised around three tissue systems and the anatomy of roots, stems and leaves in dicots and monocots. The epidermal tissue system forms the outer covering and includes epidermal cells, stomata (each with two guard cells, dumb-bell-shaped in grasses) and appendages such as root hairs and trichomes. The ground tissue system makes up the bulk of the plant and consists of parenchyma, collenchyma and sclerenchyma, occurring as cortex, pericycle, pith, medullary rays and the mesophyll of leaves. The vascular tissue system comprises xylem and phloem forming vascular bundles, which are open (with cambium, as in dicot stems), closed (without cambium, as in monocots), radial (as in roots) or conjoint. The chapter then compares the transverse sections of dicot and monocot roots and stems, noting features such as the casparian strips of the endodermis, the ring of vascular bundles in a dicot stem versus the scattered bundles in a monocot stem, and the polyarch xylem of monocot roots. Leaf anatomy distinguishes the dorsiventral dicot leaf, with palisade and spongy mesophyll, from the isobilateral monocot leaf with bulliform cells. These internal differences also reflect adaptations to the environment.