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Structure of woody plants (Vascular Cambium # (Initiation of vascular…
Structure of woody plants
Vascular Cambium
#
Fusiform Initials
Undergoing cell division produce 2 cells
continuous to be fusiform initials
Differentiates to Secondary xylem or phloem
Occasionally divide longitudinally by Anticlinal walls
Long tapered cells,140-462 micro meter in dicot and 700-8700 in conifers
Ray Initials
Short and more or less cuboidal
Undergo peiclinal cell division
produce storage parenchyma in gymnosperm
Initiation of vascular cambium
Meristem that produce the secondary plant body
Cells continue dividing instead of maturing to be a part of fascular cambium
Positioned cells never undergo cell cycle arrest
Some cells also form interfascular cambium and resume mitosis
Arrangement of cambial cells
Storied cambium
Regular horizontal rows
Non storied cambium
Irregular, without any horizontal pattern
Secondary Xylem
Heartwood and sapwood
Dark wood in the center, drier and more fragrant
Lighter wood, moister outer reason
Reaction wood
Reaction against the gravity that causes lateral stress to protect the branch
Also called tension wood in angiosperm
Growth rings
Has early wood and late wood which together forms annual ring
If tree fails to grow and still produce ring that false ring is called growth ring
Types of wood cells
Contains tracheids, vessel elements, fibers, sclererids and parenchyma
contains everything as primary xylem but no new ones
Interior of vascular cambium develops to secondary xylem called WOOD
Axial and radial system
#
Secondary Phloem
#
Equivalent cells of axial secondary xylem are arranged as early and late wood and are ring porous
Axial helps in conduction up and down the stem or root
Has axial and radial system
Forms vascular cambium during secondary growth
Outer Bark
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Initiation of cork cambia
Cork cambium arise within the cortex as a concentric layer
Initiation of first cork cambium is variable with the species
Cork and the cork cambium
Formation of new cambium also called phellogen
Differ in structure and morphogenic activity from vascular cambium
Inner cell remain cork cambium outer became cork cell
Tissue outside cork cambium comprise outer bark
Lenticels and oxygen diffusion
Develops in woody stem when epidermis is replaced by cork
Examples-: Potatoes, Apple tree, Carrots
Provide pathway for direct exchange of gases
Anomalous forms of growth
Unusual primary growth
Example-: Palm tree
No true wood, trunk would not grow radially
All primary tissue consisting of vascular bundles distributed throughout ground tissue
Anomalous secondary growth
Unequal activity of vascular cambium
Included phloem
Roots of sweet potato
Originated from phloem and worn out, acts as armor
