1 Copyright © 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 Biology Ninth Edition Kingsley Stern Chapter 6 Image Slides*

Botany Chapter 6 Stems

3 External form of a woody twig §woody twig- axis with attached leaves §node- point of leaf attachment §internode- space between nodes §blade= leaf §petiole- leaf stem §axil-angle between leaf and twig

4 Twig structure cont. §axillary bud- bud found in axil - may become branches or flowers §bud scales- protect buds §terminal 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, appendages §deciduous trees- lose their leaves annually §leaf 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

7 Fig. 6.1

8 Origin & Development of Stem §apical meristem- found at tip of stem; contributes to length §primordia- (sin. primordium)- tiny, embryonic leaves that will develop into mature leaves

9 3 primary meristems that develop from apical meristem 1. protoderm- gives rise to epidermis 2. procambium- gives rise to primary xylem & phloem, and vascular cambium 3. ground meristem- produces pith and cortex

10 Stem tissues §pith- parenchyma cells in center of stem §cortex- 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

12 Tissues cont. §Vascular cambium cont. - when dividing toward the outside, cells become sieve tube members, and companion cells

13 Tissues cont. §cork cambium- produces cork cells with suberin §cork cells make up outer bark, which prevents water loss and protects against damage §lenticels- develop beneath stomata - allow for gas exchange

14 Herbaceous Dicot stems §Vascular bundles- composed of xylem and phloem; arranged in rings

15 Monocot stems §herbaceous plants such as lilies and grasses §vascular bundles are scattered throughout the stem - xylem to the inside; phloem to the outside - surrounded by sclerenchyma cells §no cortex or pith; called fundamental tissue

16 Fig. 6.13

17 Fig. 6.5

18 Woody Dicot Stems §Annual rings- one year’s growth of xylem §Spring wood- light rings; lg. vessel elements of secondary xylem §Summer wood- dark rings; small number of vessel elements and large number of tracheids

19 Woody Dicot Stems cont. §Vascular rays- parenchyma cells that radiate out from center across the annual rings; lateral conduction

20 Fig. 6.6f2

21 Woody dicot stems cont. §heartwood- older darker wood at center; nonliving - contains resins, gums and pigments §sapwood- lighter, still-functioning xylem, closest to cambium

22 Fig. 6.9

23 Woody Dicot Stems cont. §soft wood-ex. pine (neither monocot nor dicot); no fibers §hard wood- ex. dicots such as oak and walnut §bark- all tissues outside cork cambium, including phloem

24 Specialized Stems §Rhizomes- horizontal stems that grow beneath ground - Not roots because they have scale-like leaves and axillary buds at each node and have axillary roots

25 Specialized Stems §Runners- horizontal stems that grow above ground §Stolons- grow in different directions, but not horizontally §runners and stolons are variations of the same thing

26 Specialized Stems §Tubers- underground stem; form at tips of stolons as it accumulates food - ex. potatoes - “eyes” are nodes formed in a spiral around stem §Bulbs- large buds surrounded by fleshy leaves with a small stem at the lower end – ex. Lilies and tulips

27 Specialized stems §corms- similar to bulbs, but are composed almost entirely of stem tissue - ex. gladiolus

28 Specialized stems §Tendrils- may be modified stems (ivy and grapes), or leaves (cucumbers) - help plant climb

29 Fig. 6.14

30 Wood §Wood- 50% water (by weight) §Dry wood % cellulose; % lignin §density- usually less than 1 §durability-ability to withstand decay §knots- bases of lost branches that have become covered by new annual ring

31 Wood products §lumber for construction §pulp- paper, fibers, plastic, linoleum, ice cream, bread §wood alcohol and acetic acid (vinegar) §charcoal, railroad ties, photographic film, fuel, dyes, medicines, spices and food

32 Fig. 6.3

33 Fig. 6.6f2

34 Fig. 6.4

35 Fig. 6.8

36 Fig. 6.17

37 TEXT PHOT OS

38 Fig. 6.6f1

39 Fig. 6.10

40 Fig. 6.11

41 Fig. 6.15

42 Fig. 6.p89

43 Fig. CO