Unusual Secondary Growth

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Unusual Secondary Growth

  1. 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 1
  2. 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 2
  3. 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 3
  4. 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  4

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