1. Plant Structure, Growth, and Development
Chapter 35
Plant Structure, Growth, and Development

2. Overview: Are Plants Computers?
Romanesco grows according to a repetitive program
The development of plants depends on the environment and is highly adaptive
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3. Concept 35.1: Plants have a hierarchical organization consisting of organs, tissues, and cells
Plants have organs composed of different tissues, which in turn are composed of different cell types
A tissue is a group of cells consisting of one or more cell types that together perform a specialized function
An organ consists of several types of tissues that together carry out particular functions
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4. The Three Basic Plant Organs: Roots, Stems, and Leaves
Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below ground and above ground
Plants take up water and minerals from below ground
Plants take up CO2 and light from above ground
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5. Three basic organs evolved: roots, stems, and leaves
They are organized into a root system and a shoot system
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6. Reproductive shoot (flower)
Figure 35.2
Reproductive shoot (flower)
Apical bud
Node
Internode
Apical bud
Shoot system
Vegetative shoot
Axillary bud
Blade
Leaf
Petiole
Stem
Figure 35.2 An overview of a flowering plant.
Taproot
Root system
Lateral (branch) roots

7. Monocots and eudicots are the two major groups of angiosperms
Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system
Monocots and eudicots are the two major groups of angiosperms
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8. Roots A root is an organ with important functions: Anchoring the plant
Absorbing minerals and water
Storing carbohydrates
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9. Most monocots have a fibrous root system, which consists of:
Most eudicots and gymnosperms have a taproot system, which consists of:
A taproot, the main vertical root
Lateral roots, or branch roots, that arise from the taproot
Most monocots have a fibrous root system, which consists of:
Adventitious roots that arise from stems or leaves
Lateral roots that arise from the adventitious roots
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10. In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area
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11. Figure 35.3
Figure 35.3 Root hairs of a radish seedling.

12. Many plants have root adaptations with specialized functions
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13. Storage roots Prop roots Buttress roots Pneumatophores
Figure 35.4
“Strangling” aerial roots
Storage roots
Prop roots
Buttress roots
Figure 35.4 Evolutionary adaptations of roots.
Pneumatophores

14. Stems A stem is an organ consisting of
An alternating system of nodes, the points at which leaves are attached
Internodes, the stem segments between nodes
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15. Apical dominance helps to maintain dormancy in most axillary buds
An axillary bud is a structure that has the potential to form a lateral shoot, or branch
An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot
Apical dominance helps to maintain dormancy in most axillary buds
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16. Many plants have modified stems (e. g
Many plants have modified stems (e.g., rhizomes, bulbs, stolons, tubers)
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17. Rhizomes Rhizome Root Bulbs Storage leaves Stem Stolons Stolon Tubers
Figure 35.5
Rhizomes
Rhizome
Root
Bulbs
Storage leaves
Stem
Stolons
Stolon
Figure 35.5 Evolutionary adaptations of stems.
Tubers

18. Leaves
The leaf is the main photosynthetic organ of most vascular plants
Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem
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19. Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves
Most monocots have parallel veins
Most eudicots have branching veins
In classifying angiosperms, taxonomists may use leaf morphology as a criterion
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20. Simple leaf Axillary bud Petiole Compound leaf Doubly compound leaf
Figure 35.6
Simple leaf
Axillary bud
Petiole
Compound leaf
Doubly compound leaf
Leaflet
Figure 35.6 Simple versus compound leaves.
Petiole
Axillary bud
Axillary bud
Petiole
Leaflet

21. Some plant species have evolved modified leaves that serve various functions
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22. Tendrils Spines Storage leaves Reproductive leaves Bracts Figure 35.7
Figure 35.7 Evolutionary adaptations of leaves.
Bracts

23. Dermal, Vascular, and Ground Tissues
Each plant organ has dermal, vascular, and ground tissues
Each of these three categories forms a tissue system
Each tissue system is continuous throughout the plant
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24. Dermal tissue Ground tissue Vascular tissue Figure 35.8
Figure 35.8 The three tissue systems.
Dermal tissue
Ground tissue
Vascular tissue

25. In nonwoody plants, the dermal tissue system consists of the epidermis
A waxy coating called the cuticle helps prevent water loss from the epidermis
In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots
Trichomes are outgrowths of the shoot epidermis and can help with insect defense
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26. Very hairy pod (10 trichomes/ mm2)
Figure 35.9
EXPERIMENT
Very hairy pod (10 trichomes/ mm2)
Slightly hairy pod (2 trichomes/ mm2)
Bald pod (no trichomes)
RESULTS
Very hairy pod: 10% damage
Slightly hairy pod: 25% damage
Bald pod: 40% damage
Figure 35.9 Inquiry: Do soybean pod trichomes deter herbivores?

27. The two vascular tissues are xylem and phloem
The vascular tissue system carries out long-distance transport of materials between roots and shoots
The two vascular tissues are xylem and phloem
Xylem conveys water and dissolved minerals upward from roots into the shoots
Phloem transports organic nutrients from where they are made to where they are needed
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28. The vascular tissue of a stem or root is collectively called the stele
In angiosperms the stele of the root is a solid central vascular cylinder
The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem
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29. Tissues that are neither dermal nor vascular are the ground tissue system
Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex
Ground tissue includes cells specialized for storage, photosynthesis, and support
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30. Common Types of Plant Cells
Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function
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31. The major types of plant cells are:
Parenchyma
Collenchyma
Sclerenchyma
Water-conducting cells of the xylem
Sugar-conducting cells of the phloem
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32. Parenchyma Cells Mature parenchyma cells
Have thin and flexible primary walls
Lack secondary walls
Are the least specialized
Perform the most metabolic functions
Retain the ability to divide and differentiate
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33. Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 m
Figure 35.10a
Figure Exploring: Examples of Differentiated Plant Cells
Parenchyma cells in Elodea leaf, with chloroplasts (LM)
60 m

34. Collenchyma Cells
Collenchyma cells are grouped in strands and help support young parts of the plant shoot
They have thicker and uneven cell walls
They lack secondary walls
These cells provide flexible support without restraining growth
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35. Collenchyma cells (in Helianthus stem) (LM) 5 m
Figure 35.10b
Figure Exploring: Examples of Differentiated Plant Cells
Collenchyma cells (in Helianthus stem) (LM)
5 m

36. Sclerenchyma Cells
Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin
They are dead at functional maturity
There are two types:
Sclereids are short and irregular in shape and have thick lignified secondary walls
Fibers are long and slender and arranged in threads
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37. Sclereid cells in pear (LM)
Figure 35.10c
5 m
Sclereid cells in pear (LM)
25 m
Cell wall
Figure Exploring: Examples of Differentiated Plant Cells
Fiber cells (cross section from ash tree) (LM)

38. Water-Conducting Cells of the Xylem
The two types of water-conducting cells, tracheids and vessel elements, are dead at maturity
Tracheids are found in the xylem of all vascular plants
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39. Vessel elements are common to most angiosperms and a few gymnosperms
Vessel elements align end to end to form long micropipes called vessels
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40. Tracheids and vessels (colorized SEM) Pits
Figure 35.10d
100 m
Vessel
Tracheids
Tracheids and vessels (colorized SEM)
Pits
Figure Exploring: Examples of Differentiated Plant Cells
Perforation plate
Vessel element
Vessel elements, with perforated end walls
Tracheids

41. Sugar-Conducting Cells of the Phloem
Sieve-tube elements are alive at functional maturity, though they lack organelles
Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube
Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells
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42. Sieve-tube elements: longitudinal view (LM) 3 m
Figure 35.10e
Sieve-tube elements: longitudinal view (LM)
3 m
Sieve plate
Sieve-tube element (left) and companion cell: cross section (TEM)
Companion cells
Sieve-tube elements
Plasmodesma
Figure Exploring: Examples of Differentiated Plant Cells
Sieve plate
30 m
Nucleus of companion cell
15 m
Sieve-tube elements: longitudinal view
Sieve plate with pores (LM)

43. Concept 35.2: Meristems generate cells for primary and secondary growth
A plant can grow throughout its life; this is called indeterminate growth
Some plant organs cease to grow at a certain size; this is called determinate growth
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44. Meristems are perpetually embryonic tissue and allow for indeterminate growth
Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots
Apical meristems elongate shoots and roots, a process called primary growth
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45. Lateral meristems add thickness to woody plants, a process called secondary growth
There are two lateral meristems: the vascular cambium and the cork cambium
The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem
The cork cambium replaces the epidermis with periderm, which is thicker and tougher
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46. Primary growth in stems
Figure 35.11
Primary growth in stems
Epidermis
Cortex
Primary phloem
Shoot tip (shoot apical meristem and young leaves)
Primary xylem
Pith
Vascular cambium
Secondary growth in stems
Cork cambium
Lateral meristems
Cork cambium
Axillary bud meristem
Cortex
Periderm
Primary phloem
Figure An overview of primary and secondary growth.
Pith
Secondary phloem
Root apical meristems
Primary xylem
Vascular cambium
Secondary xylem

47. Meristems give rise to:
Initials, also called stem cells, which remain in the meristem
Derivatives, which become specialized in mature tissues
In woody plants, primary growth and secondary growth occur simultaneously but in different locations
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48. This year’s growth (one year old) Leaf scar
Figure 35.12
Apical bud
Bud scale
Axillary buds
This year’s growth (one year old)
Leaf scar
Node
Bud scar
One-year-old side branch formed from axillary bud near shoot tip
Internode
Last year’s growth (two year old)
Leaf scar
Stem
Figure Three years’ growth in a winter twig.
Bud scar
Growth of two years ago (three years old)
Leaf scar

49. Flowering plants can be categorized based on the length of their life cycle
Annuals complete their life cycle in a year or less
Biennials require two growing seasons
Perennials live for many years
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50. Concept 35.3: Primary growth lengthens roots and shoots
Primary growth produces the parts of the root and shoot systems produced by apical meristems
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51. Primary Growth of Roots
The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil
Growth occurs just behind the root tip, in three zones of cells:
Zone of cell division
Zone of elongation
Zone of differentiation, or maturation
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52. Zone of differentiation Ground Root hair Vascular
Figure 35.13
Cortex
Vascular cylinder
Key to labels
Epidermis
Dermal
Zone of differentiation
Ground
Root hair
Vascular
Zone of elongation
Figure Primary growth of a root.
Zone of cell division (including apical meristem)
Mitotic cells
100 m
Root cap

53. In angiosperm roots, the stele is a vascular cylinder
The primary growth of roots produces the epidermis, ground tissue, and vascular tissue
In angiosperm roots, the stele is a vascular cylinder
In most eudicots, the xylem is starlike in appearance with phloem between the “arms”
In many monocots, a core of parenchyma cells is surrounded by rings of xylem then phloem
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54. Core of parenchyma cells
Figure 35.14
Epidermis
Cortex
Endodermis
Vascular cylinder
Pericycle
Core of parenchyma cells
Xylem
100 m
Phloem
100 m
(a)
Root with xylem and phloem in the center (typical of eudicots)
(b)
Root with parenchyma in the center (typical of monocots)
50 m
Key to labels
Figure Organization of primary tissues in young roots.
Endodermis
Pericycle
Dermal
Xylem
Ground
Phloem
Vascular

55. The innermost layer of the cortex is called the endodermis
The ground tissue, mostly parenchyma cells, fills the cortex, the region between the vascular cylinder and epidermis
The innermost layer of the cortex is called the endodermis
The endodermis regulates passage of substances from the soil into the vascular cylinder
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56. Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder
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57. 100 m Epidermis Emerging lateral root Lateral root Cortex
Figure
100 m
Epidermis
Emerging lateral root
Lateral root
Cortex
Vascular cylinder
Pericycle
Figure The formation of a lateral root. 1 2 3

58. Primary Growth of Shoots
A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip
Leaves develop from leaf primordia along the sides of the apical meristem
Axillary buds develop from meristematic cells left at the bases of leaf primordia
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59. Developing vascular strand
Figure 35.16
Shoot apical meristem
Leaf primordia
Young leaf
Developing vascular strand
Figure The shoot tip.
Axillary bud meristems
0.25 mm

60. Tissue Organization of Stems
Lateral shoots develop from axillary buds on the stem’s surface
In most eudicots, the vascular tissue consists of vascular bundles arranged in a ring
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61. Sclerenchyma (fiber cells) Ground tissue
Figure 35.17
Phloem
Xylem
Sclerenchyma (fiber cells)
Ground tissue
Ground tissue connecting pith to cortex
Pith
Epidermis
Key to labels
Epidermis
Cortex
Vascular bundles
Figure Organization of primary tissues in young stems.
Vascular bundle
Dermal
1 mm
1 mm
Ground
(a)
Cross section of stem with vascular bundles forming a ring (typical of eudicots)
(b)
Vascular
Cross section of stem with scattered vascular bundles (typical of monocots)

62. Tissue Organization of Leaves
The epidermis in leaves is interrupted by stomata, which allow CO2 and O2 exchange between the air and the photosynthetic cells in a leaf
Each stomatal pore is flanked by two guard cells, which regulate its opening and closing
The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis
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63. Surface view of a spiderwort (Tradescantia) leaf (LM) Cuticle Stoma
Figure 35.18
Guard cells
Key to labels
Stomatal pore
Dermal
Ground
Epidermal cell
50 m
Vascular
Sclerenchyma fibers
(b)
Surface view of a spiderwort (Tradescantia) leaf (LM)
Cuticle
Stoma
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Bundle- sheath cell
Figure Leaf anatomy.
Lower epidermis
100 m
Xylem
Vein
Cuticle
Phloem
Guard cells
Guard cells
Vein
Air spaces
(a) Cutaway drawing of leaf tissues
(c)
Cross section of a lilac (Syringa) leaf (LM)

64. Concept 35.4: Secondary growth increases the diameter of stems and roots in woody plants
Secondary growth occurs in stems and roots of woody plants but rarely in leaves
The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium
Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots
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65. Figure 35.19 Primary and secondary growth of a woody stem.
Primary and secondary growth in a two-year-old woody stem
Epidermis
Pith
Cortex
Primary xylem
Primary phloem
Vascular cambium
Epidermis
Primary phloem
Cortex
Vascular cambium
Primary xylem
Growth
Vascular ray
Pith
Primary xylem
Secondary xylem
Vascular cambium
Secondary phloem
Primary phloem
First cork cambium
Cork
Periderm (mainly cork cambia and cork)
Growth
Figure Primary and secondary growth of a woody stem.
Secondary phloem
Bark
Vascular cambium
Primary phloem
Secondary xylem
Late wood
Cork cambium
Early wood
Periderm
Secondary phloem
Cork
Secondary xylem (two years of production)
Vascular cambium
0.5 mm
Secondary xylem
Vascular cambium
Bark
Secondary phloem
Primary xylem
Vascular ray
Most recent cork cambium
Layers of periderm
Growth ring
Cork
(b)
Cross section of a three-year- old Tilia (linden) stem (LM)
Pith
0.5 mm

66. The Vascular Cambium and Secondary Vascular Tissue
The vascular cambium is a cylinder of meristematic cells one cell layer thick
It develops from undifferentiated parenchyma cells
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67. In cross section, the vascular cambium appears as a ring of initials (stem cells)
The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside
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68. After one year of growth After two years of growth
Figure 35.20
Vascular cambium
Growth
Vascular cambium
Secondary phloem
Secondary xylem
Figure Secondary growth produced by the vascular cambium.
After one year of growth
After two years of growth

69. Secondary xylem accumulates as wood and consists of tracheids, vessel elements (only in angiosperms), and fibers
Early wood, formed in the spring, has thin cell walls to maximize water delivery
Late wood, formed in late summer, has thick-walled cells and contributes more to stem support
In temperate regions, the vascular cambium of perennials is inactive through the winter
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70. Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age
Dendrochronology is the analysis of tree ring growth patterns and can be used to study past climate change
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71. RESULTS 2 1.5 Ring-width indexes 1 0.5 1600 1700 1800 1900 2000 Year
Figure 35.21
RESULTS 2
1.5
Ring-width indexes 1
0.5
1600
1700
1800
1900
2000
Figure Research Method: Using Dendrochronology to Study Climate
Year

72. Older secondary phloem sloughs off and does not accumulate
As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals
The outer layers, known as sapwood, still transport materials through the xylem
Older secondary phloem sloughs off and does not accumulate
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73. Growth ring Vascular ray Heartwood Secondary xylem Sapwood
Figure 35.22
Growth ring
Vascular ray
Heartwood
Secondary xylem
Sapwood
Figure Anatomy of a tree trunk.
Vascular cambium
Secondary phloem
Bark
Layers of periderm

74. The Cork Cambium and the Production of Periderm
Cork cambium gives rise to two tissues:
Phelloderm is a thin layer of parenchyma cells that forms to the interior of the cork cambium
Cork cells accumulate to the exterior of the cork cambium
Cork cells deposit waxy suberin in their walls, then die
Periderm consists of the cork cambium, phelloderm, and cork cells it produces
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75. Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air
Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm
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