unusual secondary growth
TRANSCRIPT
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UNUSUAL SECONDARY GROWTH
Unusual or anomalous secondary growth
Deviations from the usual or common pattern of secondary growth
ExamplesExamplesa. unequal activity of diff. portions of cambiumb. alteration of rel. amounts and position of vascular tissuesc. additional cambia
Significance
Taxonomic implications‐‐ atypical secondary growth can be found in certain family or genus
Ph siologicalPhysiological‐‐ found in lianas and climbing plants‐‐modified organs e.g. storage
Passiflora‐ Varied production of Xylem and phloem
Aristolochia‐ Strands of cambium produce only ray‐like parenchyma
Serjania (Sapindaceae)‐ Cambium first appears in separate strands each of which surrounds a group of vascular bundles or primary vascular bundle
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Included phloem
Nyctaginaceae, Chenopodiaceae, Amaranthaceaecambium differentiates outside the primary vascular bundles, pericycle, or inner cortical vascular bundles, pericycle, or inner cortical layersSeries of vascular cambia arise successively further outwardEach successive cambia produces X and PNew cambium develops from parenchyma cells on the outside of phloem
Bougainvilla Aristolochia
1 epidermis3 parenchyma4 cortex5 sclerenchyma7 primary phloem7 primary phloem8 primary xylem9 pith2 collenchyma6 parenchyma
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1 cork3 sclerenchyma4 phloem5 xylem7 pith7 p2 cortex6 ray
Bauhinia – unequal activity of cambium
For flexibility
Thickening of the axis in monocots
Responsible for thick axial organse.g. stems of palms
rhizomes of Musa spp.
Rapid thickening occurs below apical meristemAddition of parenchyma and vascular bundles
Primary thickening meristem
Lies below young leaf bases
PTM
Activity is independent of the apical meristemMost of the stem tissues develop from itpResponsible for most of the primary plant body
* Apical meristem plays a small part of the primary body
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PTM
Produces anticlinal rows of cells by periclinaldivisionsDerivatives– ground parenchyma traversed b bi l t dby procambial strandsAfter elongation‐‐ inrease in thickness by enlargement and division of parenchyma
Diffused secondary thickening
palmsGround tissue close to the apex expandsCentral parenchyma continue to undergo divisions which are followed by cell expansion for a long period
Secondary thickening meristem (STM)
Continuous with PTMDevelops from parenchyma cells that underwent tangential divisionProduces parenchyma outside (secondary cortex) and parenchyma and vascular bundles inside