Anatomy Prof.(Dr.) Punam Jeswal Head B.Sc ( Hons.) Part II Botany Department

Anomalous Secondary Growth In Nyctanthes

Nyctanthes is a genus of belonging to the family , native to southeastern . The name Nyctanthes means "night flowering " is a or small growing to 10 m tall flaky grey bark.

Nyctanthes Stem :- The transverse section of stem is more or less square in outline and reveals the following tissue organization from periphery towards the centre :-

Epidermis :- * Single layered epidermis consists of rectangular cells. * A Thick uninterrupted cuticle is present on the epidermis. * Many multi-cellular hairs are present.

Cortex :- * It is differentiated into collenchyma and parenchyma. * Collenchyma is several cells deep below four protruded comers while only few layers deep at the other places just beneath the epidermis. * Parenchyma is present below the collenchyma. Many intercellular spaces are present. The region extends upto vascular tissues.

Cortical Bundles :- * Four vascular bundles are present in the cortex, situated one each in each protruded bulge. * Each conical bundles faces its pointed xylem end towards outer side, i.e., epidermis. * Cortical bundles are conjoint, collateral, open and exarch. * These bundles may show secondary growth at maturity.

Endodermis : - Inner most layer of cortex is endodermis. Not well developed. Pericycle : - It is in the form of sclerenchymatous patch.

Vascular System :- * Several primary compact vascular bundles being collateral and open with endarch xylem are arranged in a ring intervene with the parenchyma in the form of rays. * vascular system consists of primary phloem, secondary phloem, cambium, secondary xylem and primary xylem. * Primary phloem is crushed and irregularly present in the patches below pericycle. * Secondary phloem is present in the form of a continuous ring and consists mainly of thick walled wood parenchyma and fibres. Tracheids and vessels are also present. * Cambium is one to three cells thick continuous layer present in between phloem and xylem. * Primary xylem is situated just near the pith facing its protoxylem towards the centre.

Pith :- It is thin walled and parenchymatous.

ABNORMALITY

Abnormality in the stem of Nyctanthes is the presence of cortical bundles apart from normal vascular bundles which occur in a ring in the centre. These cortical bundles are inversely oriented (inverted), four in number present at the four ridged portion of the stem. They are never directly connected with the main axial ring of the vascular cylinder. These are trace bundles. Cortical bundles have also been reported in some other families such as Casuarinaceae (Casuarina), Umbelliferae (Eryngium), Papilionaceae (Latkyrus marytimus), Rutaceae etc.

Fig :- The Stem Anomalous Structure - T.S. of stem of Nyctanthes arbortristis showing inversely oriented cortical vascular bundles (Abnormality). A, diagrammatic; B, detailed.