(c) Anatomy of a sporophyll

The transverse section of a fertile pinna passing through a sorus shows the internal structure of the leaflet as well as that of the sorus. The internal structure of the leaflet is differentiated into upper and lower epidermis, spongy mesophyll and vascular bundles. Both the upper and lower epidermis are single layered, non-green and covered with cuticle. Stomata are generally present in the lower epidermis only. Mesophyll tissue is spongy in nature. This is composed of thin walled, green and loosely arranged cells. The vascular bundles of lateral veins are seen in the mesophyll region. Each vascular bundle is concentric and hadrocentric (i.e., it has xylem cells in the center surrounded by the phloem cells).

The sorus is seen attached to the lower epidermis. It consists of a placenta, numerous sporangia and indusium. The placenta is a fertile tissue of colorless cells. It develops as a cylindrical out-growth from the lower epidermis and bears sporangia and an indusium. Sporangia are the spore producing organs. They develop laterally from the placenta. The indusium is a thin membrane attached at the end of the placenta which protects the sporangia in a young sorus.

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