Post on 24-Apr-2015
Members: Espinosa, Aleena
Estrada, Rico Miguel
Limbo, Carlo
Mejia, Katrina Nicole
Ongsyping, Stevenson
Thunbergia
Family Acanthaceae
Thunbergias
(common name)
Vigorous annual or
perennial vines and
shrubs growing to 2-8
meters tall
Frequent garden
escapes, becoming
invasive species
Mechanical parasites
Thunbergia
Typical Secondary Growth
Vascular Cambium
Consists of
embryonic
(incompletely
differentiated) cells
from which more
differentiated cells
originate
Lateral meristem
Produces secondary
growth in stems and
roots
Typical Secondary Growth
Secondary xylem towards the pith (inner)
Secondary phloem towards the epidermis (outer)
Periclinal additive divisions
Typical Secondary Growth
Vascular Cambium
Cells
Highly vacuolated
Large central
vacuole
Dense cytoplasm
Flat, rectangular
cells (in cross
sections)
Modified vascular cambium
• Death of the cambium
- strands of vascular cambium cease to function
Certain regions of the cambium begin to produce mostly parenchyma inside, resulting in a wavy outline of the secondary xylem, while adjacent regions of the cambium do not
Unequal activity of the cambium
1. x’s of Thunbergia
Taken from Ms. Erika Alvero Bascos
2. x’s of Thunbergia. Taken from Ms. Erika Alvero Bascos
Modified vascular cambium Conjunctive tissue
- the patches of parenchyma
- do not extend very far radially because
cambium returns back to normal, producing
secondary xylem
- within it, small areas become mitotically active
differentiate into included phloem
* Included phloem
- any secondary phloem located interior to
secondary xylem
Modified vascular cambium
Anomalous placement of the cambium
- margins of new cambial strands fuse with the older ones to continue functioning normally continuous vascular cambium persists
Presence of successive cambia • New cambial strands develop in outer phloem
parenchyma• Secondary xylem is still produced towards the
inside, enclosing secondary and old(?) phloem- results in multiple layers of secondary
xylem
Advantages and Modifications of
Anomalous Secondary Growth
Increased stem flexibility
Protects the phloem
Increases storage parenchyma
Reduces chances of disturbing translocation of
materials to the roots
Counteracts stress and strains caused by natural
forces when clinging to supports
Limits physical disruption of vascular tissues during
twisting and bending
Advantages and Modifications of
Anomalous Secondary Growth
Rapid vigorous regeneration of tissues
For wound healing (i.e. after girdling)
Evolution of wider vessels and sieve tubes
Reduced xylem areas are compensated hydraulically
Fewer cambial initials in vines
Less xylem production = the vascular cambium does
not expand in circumference nearly as much as trees
or shrubs
ReferencesBio 101 Plant Morpho-anatomy Laboratory Manual
Dobbins, D.R. and Fisher, J.B. (1986). Wound Responses In Girdled Stems of Lianas. Botanical Gazette 147
Ewers, F.W. and Fisher, J.B. (1990). Why Vines Have Narrow Stems: Histological Trends in Bauhinia (Fabaceae). New York: Springer.
Fahn, A. (1990). Plant Anatomy, 4th Edition. Oxford: Butterworth-Heineman Ltd.
Fisher, J.B. and Ewers, F.W. (1992). Xylem Pathways in Liana Stems With Variant Secondary Growth. Botanical Journal of the Linnean Society 108
Varghese, T.M. (1987). An Introduction to the Anatomy of Angiosperms. New Delhi: Allied Publishers Limited.