c) Anatomy of leaflet

Figure 15.9 shows a transverse section of a Cycas leaflet (pinna). It has a number of anatomical peculiarities. Some of these are xerophytic characteristics. The general internal organization of tissues is similar to a dorsoventral leaf. The upper epidermis has a thick cuticle but without stomata. The lower epidermis has a thin cuticle and depressed, protected stomata. Sclerenchymatous hypodermis is present under the entire upper epidermis but is restricted to the midrib region of the lower epidermis. Mesophyll tissue is differentiated into upper palisade and lower spongy mesophyll. A special tissue present in the lamina is called transfusion tissue and is located in between the palisade and spongy mesophyll. It extends laterally from the midrib into the lamina on either side and helps in lateral conduction in the absence of lateral veins. The vascular bundle of the midrib is conjoined and collateral with phloem towards the lower and xylem towards the upper epidermis. It is enclosed in a parenchymatous bundle sheath. The xylem is triangular in shape. It is mesarch with centripetal and centrifugal metaxylem.

d) Reproduction

ACycas plant is a diploid sporophyte and shows asexual reproduction by formation of spores. Cycas is heterosporous and strictly dioecious (i.e. each plant produces only male or only female reproductive organs). The microsporophylls are produced on the male plant and the megasporophylls are produced on the female plant.

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