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1Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
*See PowerPoint Lecture Outline for a complete, ready-made presentation integrating art and lecture notes.
Introductory Plant BiologyNinth Edition
Kingsley Stern
Chapter 6
Image Slides*
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External form of a woody twigwoody twig- axis with attached
leavesnode- point of leaf attachmentinternode- space between nodesblade= leafpetiole- leaf stemaxil-angle between leaf and twig
4
Twig structure cont.axillary bud- bud found in axil - may become branches or flowersbud scales- protect budsterminal bud- bud at tip of twig - meristematic tissue that increases length of twig - counting bud scale scars of terminal
buds determines age of twig
5
Twig structure cont.stipules- paired, often leaf-like,
appendagesdeciduous trees- lose their leaves
annuallyleaf scar- mark left by leaf after it
falls
6
Twig Structure cont.bundle scar- mark vascular tissue
on leaf scar - usually 3 - identify the tree in winter
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Origin & Development of Stemapical meristem- found at tip of
stem; contributes to lengthprimordia- (sin. primordium)- tiny,
embryonic leaves that will develop into mature leaves
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Stem tissuespith- parenchyma cells in center of
stemcortex- parenchyma cells inside
epidermis; may produce food if chlorophyll is present
Both function in food storage
11
Tissues cont.Vascular cambium- narrow band
of cells between primary xylem and phloem
- lateral meristem - when dividing toward the center, cells become tracheids, vessel elements and fibers
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Tissues cont.Vascular cambium cont. - when dividing toward the outside, cells become sieve tube members, and companion cells
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Tissues cont.cork cambium- produces cork cells
with suberincork cells make up outer bark,
which prevents water loss and protects against damage
lenticels- develop beneath stomata - allow for gas exchange
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Monocot stemsherbaceous plants such as lilies and
grassesvascular bundles are scattered
throughout the stem - xylem to the inside; phloem to the outside - surrounded by sclerenchyma cellsno cortex or pith; called
fundamental tissue
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Woody Dicot StemsAnnual rings- one year’s growth of
xylemSpring wood- light rings; lg. vessel
elements of secondary xylemSummer wood- dark rings; small
number of vessel elements and large number of tracheids
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Woody Dicot Stems cont.Vascular rays- parenchyma cells
that radiate out from center across the annual rings; lateral conduction
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Woody dicot stems cont.heartwood- older darker wood at
center; nonliving - contains resins, gums and pigmentssapwood- lighter, still-functioning
xylem, closest to cambium
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Woody Dicot Stems cont.soft wood-ex. pine (neither
monocot nor dicot); no fibershard wood- ex. dicots such as oak
and walnutbark- all tissues outside cork
cambium, including phloem
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Specialized StemsRhizomes- horizontal stems that
grow beneath ground - Not roots because they have
scale-like leaves and axillary buds at each node and have axillary roots
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Specialized StemsRunners- horizontal stems that
grow above groundStolons- grow in different
directions, but not horizontallyrunners and stolons are variations
of the same thing
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Specialized StemsTubers- underground stem; form at
tips of stolons as it accumulates food - ex. potatoes
- “eyes” are nodes formed in a spiral around stemBulbs- large buds surrounded by
fleshy leaves with a small stem at the lower end – ex. Lilies and tulips
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Specialized stemscorms- similar to bulbs, but are
composed almost entirely of stem tissue
- ex. gladiolus
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Specialized stemsTendrils- may be modified stems
(ivy and grapes), or leaves (cucumbers)
- help plant climb
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Wood Wood- 50% water (by weight)Dry wood- 60-75% cellulose; 12-
25% lignindensity- usually less than 1durability-ability to withstand
decayknots- bases of lost branches that
have become covered by new annual ring
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Wood productslumber for constructionpulp- paper, fibers, plastic,
linoleum, ice cream, breadwood alcohol and acetic acid
(vinegar)charcoal, railroad ties,
photographic film, fuel, dyes, medicines, spices and food