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The Stem
The axis of plant that originates above the hypocotyl of the embryo in the seed
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g
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- some stem are specialized for storage, reproduction and other purposes
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The falling of leaves is a natural phenomenon, it is the result of the formation of abscission layer of
special cells at the base of the petiole, the point where it is attached to the stem
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3 TYPES OF STEM
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
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dicotyledonous woody
dicotyledonous herbaceous herbaceous
monocotyledonous

Longitudinal section of woody dicot :
From the very tip of the stem, 3 regions are recognized:
 region of meristematic activity - the area of promeristem of primordial stem (youngest
part of the apical meristem)

2 REGIONS OF PROMERISTEM (based of Corpus- Tunica Theory):
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

Tunica - outer enveloping layer of cells which divide at right angles to the surface (anticlinal
division)
Corpus- central core, composed of cells which divide parallel to the surface (periclinal division)
 region of elongation - extends from the base of the bud downward through several
nodes and internodes
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pericycle - parenchyma and collenchyma cells
*The sclerenchyma forms an isolated group opposite the
vascular bundles
II
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- consisting of circular row of meristematic cells which
form secondary vascular tissues as the stem grows
older, thus resulting growth of stem diameter
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b
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2
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Is the dead part of the wood
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The living part of the wood
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2
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epidermis – persistent
cortex – almost indistinct
stele – with vascular bundle and ground parenchyma (scattered outside the vascular bundles)



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