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Introductory Plant BiologyNinth Edition

Kingsley Stern

Chapter 6

Image Slides*

Botany Chapter 6

Stems

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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

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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

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Twig structure cont.stipules- paired, often leaf-like,

appendagesdeciduous trees- lose their leaves

annuallyleaf scar- mark left by leaf after it

falls

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Twig Structure cont.bundle scar- mark vascular tissue

on leaf scar - usually 3 - identify the tree in winter

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Fig. 6.1

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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

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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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Herbaceous Dicot stemsVascular bundles- composed of

xylem and phloem; arranged in rings

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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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Fig. 6.13

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Fig. 6.5

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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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Fig. 6.6f2

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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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Fig. 6.9

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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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Fig. 6.14

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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

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Fig. 6.3

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Fig. 6.6f2

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Fig. 6.4

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Fig. 6.8

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Fig. 6.17

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TEXT PHOT

OS

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Fig. 6.6f1

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Fig. 6.10

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Fig. 6.11

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Fig. 6.15

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Fig. 6.p89

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Fig. CO