Anatomy of Cycas Stem: Primary and Secondary Structure

Part – 2: Anatomy of  Cycas
<<< Part 1    —-     Part 3 >>>

Anatomy of Cycas

Cycas Stem Primary Structure

Ø  Anatomy of the stem of Cycas resembles that of dicot plants.

Ø  The T.S. of the stem is irregular in outline due to the presence of persistent leaf bases and leaf scars.

Ø  Cortex very large and composed of loosely packed parenchymatous cells.

Ø  Vascular tissue consists of many vascular bundles arranged as a ring.

Ø  Each vascular bundle is open and endarch.

Ø  The Pith very large and parenchymatous.

Ø  Many mucilage canals and leaf traces present in the cortex.

Ø  Cortical and pith parenchyma contain plenty of starch grains.

Ø  Numerous leaf traces are present in the cortex of Cycas.

Ø  The Leaf traces in Cycas are called as girdles (or girdle traces).

Ø  Leaf traces are concentric and mesarch.

Leaf Trace (Girdles) in Cycas

Ø  Cycas shows girdling of leaf traces, as explained below.

Ø  Parenchymatous leaf gaps are present in Cycas, hence leaves are macrophyllous.

Ø  Each leaf receives FOUR supplies from TWO vascular bundles from the stem.

Ø  Each leaf receives FOUR traces (from two vascular bundles).

You may also like: Cycas PPT (Download)

Ø  Among the four traces, two are direct, the other two passes around the stem though the cortex (these traces are called girdle traces)

Ø  Leaf traces are concentric and endarch when they start and mesarch when they pass out the cortex.

Ø  Due to this particular girdling pattern of leaf traces, we can see plenty of leaf traces in the cross section of the stem of Cycas.

Ø  The presence of concentric bundles is a Pteridophytic character which shows the affinity between Cycas and ferns.

Secondary Thickening of Cycas Stem

Ø  Secondary thickening is present in the stem and tap-root of Cycas.

Ø  Cycas shows Anomalous Secondary thickening in the stem.

Ø  The first cambial ring (formed by the fusion of fascicular and inter-fascicular cambium) stays active for a short period time.

Ø  This cambium cut secondary xylem towards the inner side and secondary phloem towards the outer side.

Ø  After a short time, a new discontinuous cambial ring is originated outside the secondary phloem.

Ø  The second cambium then cut secondary xylem and phloem for some time and then it also perishes.

Ø  This process is repeated throughout the lifetime of Cycas.

Ø  Thus, secondary xylem and phloem are produced in successive rings. The older ring will be inner and the younger one will be outer.

Ø  The growth pattern is NOT annual in Cycas and hence these rings are NOT annular rings.

Ø  They can be called as just growth rings.

Ø  The wood of Cycas is manoxylic type

Ø  Manoxylic wood: A wood with large amount of paranchymatous cells.

<<< Cycas Part 1      |      Cycas Part 3: Anatomy of Root & Coralloid Root >>>