Division: Cycadophyta Order: Cycadales Family: Cycadaceae Genus: Cycas

T.S. Coralloid Root of Cycas revoluta

The outer layer is called the Epiblema or Exodermis when young; when the root is older the outer layer is called the Periderm.

Next to this is the parenchymatous Outer Cortex.

There is a broad conspicuous blue-green zone (may be stained a translucent brown) present in the middle of the cortex. This is the Algal Zone. It lies midway between the vascular bundle and the epiblema. The cortical cells within this region get disorganised and are inhabited by blue-green algae (Cyanobacteria) such as Nostoc & Anabaena spp.

Cortex and vascular tissues are separated by a single-layered Endodermis, followed by a many-layered Pericycle.

Vascular bundles are radial and Xylem triarch and exarch (where the oldest xylem tissues are located away from the axis).

Secondary growth is very minimal if present, but is generally absent.

Division: Cycadophyta Order: Cycadales Family: Cycadaceae Genus: Cycas

T.S. Leaf of Cycas circinalis

In the lamina region the Mesophyll tissue is differentiated into (upper) Palisade and (lower) Spongy Parenchyma.

Xylem is mesarch (i.e. Protoxylem lies in the middle & Metaxylem is on either side).

Towards the upper side of the VB the xylem is well developed and forms Centripetal Xylem with distinct proto- and meta- xylem.

The lower side of the VB has small vascular strands detached from the centripetal xylem to form Centrifugal Xylem (containing only metaxylem).

In between the centripetal and centrifugal xylem, parenchyma is present.

Division: Cycadophyta Order: Cycadales Family: Cycadaceae Genus: Cycas

T.S. Cycas Leaf Rachis

Division: Cycadophyta Order: Cycadales Family: Cycadaceae Genus: Cycas

Cycas Leaf Rachis cont’d

It is cylindrical in outline, showing insertion of pinnae on the adaxial (upper) side.

The rachis is differentiated into Epidermis, Hypodermis, Ground tissue & a ring of vascular bundles.

Epidermis is single layered, thickly cuticularised and is amphistomatic (i.e. interrupted by stomata throughout its surface).

The hypodermis is mainly composed of thick-walled cells. Intermixed with these cells are a few cells having chloroplasts (Chlorenchyma).

This chlorenchymatous hypodermis is 2-3 layered toward adaxial side and many layered toward abaxial (lower) side and is followed by parenchyma ground tissue with many mucilage ducts.

The VBs are arranged in an inverted omega (Ω) shaped arc. Each VB remains surrounded by a thick walled, single layered bundle sheath & is conjoint, collateral & open.

The arrangement of the xylem and phloem differs in VBs at the base, central & upper region of the rachis.

o Higher up and for the most part of the rachis, the VBs are diploxylic (i.e. 2 types of xylem elements exist – centripetal & centrifugal xylem). The centripetal xylem is large and triangular, while 2 small groups of centrifugal xylem lying on both sides. The phloem is towards the adaxial side of the rachis.

o At the very base of the rachis, VBs show only centrifugal xylem which is endarch. The phloem occupies similar position towards the adaxial side of the rachis.

o A little higher up the base of the rachis, VBs show centrifugal xylem towards the abaxial side and centripetal xylem towards the adaxial side. In the centre of these two xylem groups, protoxylem is present (this condition is said to be Mesarch).

Division: Cycadophyta Order: Cycadales Family: Cycadaceae Genus: Cycas

T.S. Cycas Microsporophyll (Male Sporophyll)

The Microsporangia (pollen/spore sacs), within which develop the microspores, are borne on the abaxial (lower) side of the Microsporophyll.

Division: Cycadophyta Order: Cycadales Family: Cycadaceae Genus: Cycas

L.S. Cycas Archegonia