Anatomy of Flowering Plants
- Secondary growth in dicot root:
- Secondary growth is found only in dicots which enhances secondary lateral meristem to increase the circumference / girth of a plant. Exception: Palm, Yucca, smilax, coconut.
- Stage I : Conjunctive parenchyma becomes meristematic and give rise to secondary Xylem and Phloem.
- Stage II : Conjunctive parenchyma cells form a wavy band.
- Stage III: Primary Vascular rays / medullary rays from pericycle is formed opposite to protoxylem ends.
- Stage IV: Ring of vascular cambium gives secondary Xylem and Phloem.
- Secondary growth in dicot stem:
- Secondary vascular tissues are formed by vascular cambium that is produced by Fascicular and Interfascicular cambium.
- Vascular cambium undergoes additive and multiplicative division to undergo dilation. [Movement of Vascular cambium gradually outside by adding new cells].
- 2 cells of vascular cambium (i) Ray initials and (ii) Fusiform initials which develop secondary Xylem inside and secondary phloem out side.
- Secondary Xylem forms the bulp of the wood, where it has no distinction into proto and meta xylem.
- Width of 2nd Xylem grows with the age.
- Yearly growth is distinct in the areas with 2 seasons.
|Soft wood(gymnosperm wood)||Hard wood (dicot wood)|
|→ devoid of vessels||→ Porous wood two types|
|→ Non porous||→ (i) Ring porous. → Eg: Cassia fistula,|
|→ Easy porous||→ (ii) Diffuse porous. Eg: Sihyzinium cumini|
|→ Eg: Cedrus, Pinus|
- Sap wood: → Outer light coloured
Heart wood: → Inner dark coloured
- Annual / yearly growth appear in the form of annual ring. Shedy of age of trees with regard to the annual rings is called dendrochronology.
- Periderm formation = Phellogen → (aerating pore) + Phellem + Phelloderm
- All dead cells lying outside phellogen is called bark [which acts as insect repellent / fire proof] which is of 2 types (i) hard / soft.
View this video for the topic from 3:50 to 54:48
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