1. 2/17/2010
Unusual or anomalous
secondary growth
Deviations from the usual or common
pattern of secondary growth
Examples
a. unequal activity of diff. portions of
cambium
UNUSUAL SECONDARY GROWTH b. alteration of rel. amounts and position of
vascular tissues
c. additional cambia
Significance Passiflora
‐ Varied production of Xylem and phloem
Taxonomic implications
‐‐ atypical secondary growth can be found in certain
family or genus
Physiological
Ph siological
‐‐ found in lianas and climbing plants
‐‐ modified organs e.g. storage
Aristolochia Serjania (Sapindaceae)
‐ Strands of cambium produce only ray‐like ‐ Cambium first appears in separate strands
parenchyma each of which surrounds a group of vascular
bundles or primary vascular bundle
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2. 2/17/2010
Included phloem
Nyctaginaceae, Chenopodiaceae,
Amaranthaceae
cambium differentiates outside the primary
vascular bundles, pericycle, or inner cortical
layers
Series of vascular cambia arise successively
further outward
Each successive cambia produces X and P
New cambium develops from parenchyma
cells on the outside of phloem
Bougainvilla Aristolochia
1 epidermis
3 parenchyma
4 cortex
5 sclerenchyma
7 primary phloem
8 primary xylem
9 pith
2 collenchyma
6 parenchyma
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3. 2/17/2010
1 cork
3 sclerenchyma
4 phloem
5 xylem
7 p
pith
2 cortex
6 ray
Bauhinia – unequal activity of Thickening of the axis in
cambium monocots
Responsible for thick axial organs
For flexibility e.g. stems of palms
rhizomes of Musa spp.
Rapid thickening occurs below apical
meristem
Addition of parenchyma and vascular bundles
Primary thickening meristem PTM
Lies below young leaf bases
Activity is independent
of the apical meristem
Most of the stem
tissues develop from it
p
Responsible for most
of the primary plant
body
* Apical meristem plays
a small part of the
primary body
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4. 2/17/2010
PTM
Produces anticlinal rows of cells by periclinal
divisions
Derivatives– ground parenchyma traversed
by procambial strands
b bi l t d
After elongation‐‐ inrease in thickness by
enlargement and division of parenchyma
Diffused secondary Secondary thickening
thickening meristem (STM)
palms Continuous with PTM
Ground tissue close to the apex expands Develops from parenchyma cells that
Central parenchyma continue to undergo underwent tangential division
divisions which are followed by cell expansion Produces parenchyma outside (secondary
for a long period cortex) and parenchyma and vascular
bundles inside
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