The Sporophyte

The sporophyte generation is an asexual diploid (2n) phase. It begins with the zygote after fertilization takes place. The adult is represented by the fern plant (i.e., adult sporophyte).

External morphology: The adult sporophyte (fern plant) is a perennial evergreen herb. It is differentiated into true roots, a stem and leaves (Fig. 15.1). The plant has a well developed vascular system.

• The stem is represented by a rhizome and stolons.

• The main stem is an underground rhizome. It is hard, woody and dark colored. The rhizome grows obliquely erect and is covered with persistent bases of fallen leaves. It produces green aerial leaves and lateral branches called stolons. The main function of the rhizome is perennation.

• Stolons are the sub-aerial, lateral branches of the rhizome. These spread in all directions and produce new fern plants through vegetative propagation. Each stolon is slender and cylindrical with a smooth surface. Adventitious roots are known to develop from stolons.

• Nephrolepis has well-developed, adventitious, fibrous roots. These are branched and help in fixation and absorption.

• Fern leaves are large, green and aerial. They develop from the rhizome. Young leaves are delicate, coiled like a spring and show circinnate vernation. These are covered with numerous scales called ramenta. Scales protect the young leaves and fall off as the leaves mature.

A fully formed mature leaf is commonly called a fern frond. It is upto 5 feet long and unipinnately compound. The frond has a long petiole. The main rachis bears numerous leaflets (pinnae) arranged in two rows. Each leaflet is linear, broad at the base and tapering towards the apex. It has a midrib with many forked lateral veins. Hydathodes or water stomata are present at the ends of lateral veins on the upper surface of each leaflet. These appear as minute spots and help in removing excess of water and salts from the plant by guttation. The exuded salts get deposited on hydathodes and form white spots. Hence, hydathodes are called chalk glands.

The fern plant is a diploid sporophyte. It shows asexual method of reproduction by spore formation. The spore producing structures are called sori. These develop on the lower surface of leaflets. Leaves with sori are called sporophylls.

Table of Contents

15.0 - Introduction
15.1 Pteridophyta : General Account
15.2 Gymnosperms
15.3 Angiosperms : Dicotyledons
15.4 Angiosperms : Monocotyledons
15.5 Vascularization
15.6 Development of seed habit
15.7 Development of Flower and Fruit

Chapter 16