Nodal anatomy, Leaf development & Phyllotaxy

Nodal anatomy of leaves& it's developement, Phyllotaxy - Arrangements of leaves

1. NODAL ANATOMY

2. NODAL ANATOMY Shoots consists of stems bearing leaves. The point where the leaf attached to the stem called Node . ( site of attachment of leaves to the stem ) The distance between two nodes on the shoot is called Vegetative Internodes .

3. LEAF TRACES Leaves must have access to a source of water and essential minerals. This transport of substances takes place in primary vascular connections between the stem vascular system and the base of leaves called Leaf traces . Leaf traces are composed of protoxylem , metaxylem , protophloem and metaphloem .

4. Typically contains transfer cells in both primary xylem and primary phloem .

5. LEAF GAP The continuity of the cylinder of primary vascular tissue is broken immediately above the position of outward divergence of leaf trace, leaving a discontinuity is called Leaf Gap. Since, these leaf gaps doesn’t affect vascular system. Lateral connectivity between tissues on top and bottom of the leaf gap is formed, since vascular system connectivity is breaked due to leaf gaps.

6. PHYLLOTAXY

7. PHYLLOTAXY “ Phyllotaxis ” or “ Phyllotaxy ” is the arrangement of leaves on a stem. The word phyllotaxy is derived from ancient Greek word. ( Phyllo means leaf and taxis means arrangements ) Phyllotaxy in mature plants is directly related to the position & size of leaf primordia produced on apical meristems of varying size and shape.

8. TYPES OF PHYLLOTAXY Based on the number of leaves and arrangement of leaves from the nodes, the phyllotaxy has various types. Alternate Opposite Whorled

9. Alternate Phyllotaxy When only one leaf develops at each node. Eg : Brassica campestris Based on the position of leaves at after particular number of leaves, alternate phyllotaxy is further subdivided into two. Distichous Tristichous

10. A) Distichous : When 3 rd leaf comes over the first one. Eg ; Grasses. B) Tristichous : When 4 th leaf comes over the first one. Eg ; Cypres .

11. Opposite Phyllotaxy When a pair of leaves are present just opposite to each other at each node, eg ; Calotropis . There are two types in opposite phyllotaxy . Opposite Deccusate Opposite Superposed A) Oppposite Decussate: When two successive pairs of leaves occur at right angle to each other, eg ; Psidium gujava .

12. B) Opposite Superposed: When all pairs of leaves occur in same plane. Eg ; Combretum .

13. Whorled Phyllotaxy When more than two leaves are arranged in the form of whorl at each node, the phyllotaxy is called Whorled . Eg ; Hydrilla verticillata , Nerium etc.,