botany lecture - chapter 5 and 8

7/27/2019 Botany Lecture - Chapter 5 and 8

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STEMS AND FUNCTIONS


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provide a framework for leaves, flowers

and seeds.

carry water and minerals from the soil, and

sugars manufactured in leaves throughout

the plant.

MAJOR FUNCTIONS OF THE STEM


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ECONOMIC IMPORTANCE


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Horticulture ,

landscaping and bonsai

making

History,Culture and

Economics

ECONOMIC IMPORTANCE


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(Curcuma longa)-luyang dilaw

ECONOMIC IMPORTANCE

hops (Humulus lupu lus).-

Beer flavor

Cinnamon bark

cinnamon bread


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Parts of a Stem


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Parts of a Stem


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STEM GROWTH AND DIFFERENTIATION


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STEM GROWH AND DIFFERENTIATION


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The three sections in young dicot stem are dermal, cortex

and stele.


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Cross section of

young dicot stem

A young dicot stem has eustele a true stele.


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Monocot stem shows dermal and ground tissue sections.

The arrangement of vascular bundles is scattered.


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Monocot stem

Vascular bundle in monocot stem is enclosed by bundle

sheath


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Dicot stem has eustele

Monocot stem has dispersed bundles


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EUSTELE

With loose ring

of vascular

bundles

From Root Protostele to stem eustele


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VASCULAR CAMBIUM

o Initiation of the vascular cambium

VASCU AR CAMBIUM


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VASCULAR CAMBIUM

Fusiform initials

Ray initials

Ray initials

Fusiform initials

1. Storage parenchyma2. Albuminous cells

1. tracheids, vessel

elements and fibers

2. Sieve cells, sieve tube

members, companion

cells, fibers

S d G th


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Presence of secondary growth

Modern ferns Absent in all

species

Gymnosperms Present in all

species

Dicots Present in manyspecies, other

species are

herbs

Monocots Ordinary type is

absent in many

species, somehave anomalous

secondary

growth

Secondary Growth

VASCULAR CAMBIUM PRODUCES SECONDARY XYLEM


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VASCULAR CAMBIUM PRODUCES SECONDARY XYLEM

AND PHLOEM


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Region of secondary vascular tissues

Old di d l i


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Vascular cambium

Secondary xylem

Primary xylem

pith

Secondary phloem

Primary phloem

Old dicot stem secondary vascular tissues

S d X l T f W d C ll


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Secondary Xylem Types of Wood Cells

Axial System from fusiform initials

Radial System ray initials

Fibers and vessels in Wood

SECONDARY XYLEM


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SECONDARY XYLEM

1. Types of Wood Cells derived from fusiform initials and ray initials

fusiform initialsaxial system

ray initialsradial system

SECONDARY XYLEM


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SECONDARY XYLEMGrowth Rings a.k.a. Annual Ring

1. Early Woodspring wood

2. late woodsummer wood

SECONDARY XYLEM


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Darkening of the Heartwood

1. Breakage of water columns in

tracheary elements (freezing, windvibration, etc)

2. Fungal attack

3. Formation of tylosis

4. Metabolic changes that produce

phenolic compounds, lignins,aromatic compounds

SECONDARY XYLEM

HEARTWOOD AND SAPWOOD

SECONDARY XYLEM


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SECONDARY XYLEM

REACTION WOOD

Angiosperm: Tension Wood

Upper side of stem produces many

special gelatinous fibers whose walls

are rich in cellulose

Gymnosperm : Compression Wood

Underside of the branch produces

fibers whose walls are rich in lignin.

SECONDARY PHLOEM


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SECONDARY PHLOEM

INNER BARK

OUTER BARK or PERIDERM


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Cork and the Cork Cambium



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lenticel

phellemPhellogen or

Cork cambium

Phelloderm orCork

parenchyma


Cork and the Cork Cambium

VARIABILITY OF THE OUTER BARK


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VARIABILITY OF THE OUTER BARK

LENTICELS AND OXYGEN DIFFUSION


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LENTICELS AND OXYGEN DIFFUSION

Pine stems have resin ducts


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Pine stems have resin ducts

ANOMALOUS FORMS OF GROWTH


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1. Anomalous Secondary Growth in potato

Formation of cambia

around the vesselsAdvantage: speed the production of storage

capacity in storage roots and stems



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Included phloemtype of secondary phloem located between two bands

of xylem

Selective advantage may be protection of phloem from insects by one to

several layers of wood



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3. Secondary Growth in Monocots

Joshua tree (Yucca brevifolia)

Outermost cells

of secondary

vascular bundles

develop into

fibers with thick

secondary walls.

Modified stems


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Modified stems

Onion

Bulb short stem covered with fleshy blades

Function storage and reproduction

Modified stems


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Cactus

Cladodes- green stemPhotosynthesis

Reproduction

storage

Rhizome- scaly underground stem

Reproduction

storage

Modified stems

Modified stems


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Tubers

swollen outgrowths of stolon for

storage and reproduction

Hooks for protection in stem of rose

Modified stems

Modified stems


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Stolons-horizontal stems with

adventitious buds

for reproduction of new plants

Modified stems

Modified stems


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Gabi or taro

Corm

vertical and shortunderground stem

reproduction

storage

Twinerclimbing/twining

stem support

Modified stems

botany lecture - chapter 5 and 8

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