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.