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CHAPTER 35
PLANT STRUCTURE
AND GROWTH
I. INTRODUCTION TO MODERN PLANT BIOLOGY
A.
B.
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MOLECULAR BIOLOGY IS REVOLUTIONIZING THE
STUDY OF PLANTS
PLANT BIOLOGY REFLECTS THE MAJOR THEMES IN
THE STUDY OF LIFE
THE CORRELATION BETWEEN STRUCTURE AND
FUNCTION AND THE EVOLUTIONARY CONTEXT OF
ADAPTATION TO THE ENVIRONMENT ILLUMINATE
OUR STUDY OF PLANTS.
II. THE ANGIOSPERM BODY
A.
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PLANT'S ROOT AND SHOOT SYSTEMS
ARE EVOLUTIONARY ADAPTATIONS
TO LIVING ON LAND
ROOTS ANCHOR ABSORB AND
CONDUCT WATER AND MINERALS, AND
STORE FOOD.
THE SHOOT SYSTEM CONSISTS OF
STEMS, LEAVES, AND FLOWERS.
LEAVES ARE ATTACHED BY THEIR
PETIOLES TO THE NODES OF THE
STEM, LEAVES AND FLOWERS WITH
INTERNODES OF THE STEM
SEPARATING THE NODES.
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AXILLARY BUDS, LOCATED IN THE AXILS OF
PETIOLES AND STEMS, HAVE THE POTENTIAL
TO EXTEND AS VEGETATIVE OR FLORAL
BRANCHES.
VASCULAR TISSUES INTEGRATE THE PARTS OF
THE PLANT.
WATER AND MINERALS MOVE UP FROM ROOTS
IN THE XYLEM.
SUGAR IS TRANSPORTED FROM THE LEAVES OR
STORAGE ORGANS IN THE PHLOEM.
THE PLANT BODY IS DIVIDED INTO A ROOT
SYSTEM AND A SHOOT SYTEM, CONNECTED BY
VASCULAR TISSUE THAT IS CONTINUOUS
THROUGHOUT THE PLANT.
THE ROOT SYSTEM
 THE SHOOT SYSTEM

– STEMS
– LEAVES
A. STRUCTURAL ADAPTATIONS OF PROTOPLASTS AND
WALLS EQUIP PLANT CELLS FOR THEIR SPECIALIZED
FUNCTIONS
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PARENCHYMA CELLS, RELATIVELY UNSPECIALIZED CELLS THAT
RETAIN THE ABILITY TO DIVIDE, PERFORM MOST OF THE
PLANT'S METABOLIC FUNCTIONS OF SYNTHESIS AND STORAGE.
COLLENCHYMA CELLS, WHICH HAVE UNEVENLY THICKENED
CELL WALLS, SUPPORT YOUNG, GROWING PARTS OF THE PLANT.
SCLERENCHYMA CELLS, FIBERS AND SCLEREIDS, HAVE THICK,
LIGNIFIED WALLS THAT HELP SUPPORT MATURE, NONGROWING PARTS OF THE PLANT.
TRACHEIDS AND VESSEL ELEMENTS, THE WATERCONDUCTING CELLS OF XYLEM, HAVE THICK WALLS AND ARE
DEAD AT FUNCTIONAL MATURITY.
SIEVE-TUBE MEMBERS ARE THE SUGAR TRANSPORTING CELLS
OF PHLOEM. THOUGH ALIVE AT FUNCTIONAL MATURITY,
SIEVE-TUBE MEMBERS DEPEND ON THE SERVICES OF
NEIGHBORING COMPANION CELLS.
C.
THE CELLS OF A PLANT ARE ORGANIZED INTO
DERMAL, VASCULAR, AND GROUND TISSUE SYSTEMS

DERMAL TISSUE (EPIDERMIS),
VASCULAR TISSUE (XYLEM AND
PHLOEM), AND GROUND TISSUE
(MOSTLY PARENCHYMAL CELLS)
ARE CONTINUOUS THROUGHOUT
THE PLANT, ALTHOUGH IN THE
VARIOUS PLANT ORGANS THEY
DIFFER IN ARRANGEMENT AND IN
SOME SPECIALIZED FUNCTIONS.
III. PLANT GROWTH
A. MERISTEMS GENERATE CELLS FOR NEW
ORGANS THROUGHOUT THE LIFETIME
OF A PLANT: AN OVERVIEW OF PLANT
GROWTH
 APICAL MERISTEMS ELONGATE SHOOTS
AND ROOTS THROUGH PRIMARY GROWTH.
 LATERAL MERISTEMS ADD GIRTH TO
WOODY PLANTS THROUGH SECONDARY
GROWTH.
B. PRIMARY GROWTH: APICAL MERISTEMS EXTEND
ROOTS AND SHOOTS BY GIVING RISE TO THE PRIMARY
PLANT BODY
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APICAL MERISTEMS PRODUCE CELLS THAT CONTINUE TO
DIVIDE AS MERISTEMATIC CELLS OF THE PROTODERM,
PROCAMBIUM, AND GROUND MERISTEM.
THESE PRIMARY MERISTEMS GIVE RISE TO THE DERMAL,
VASCULAR, GROUND TISSUES OF THE PRIMARY PLANT
BODY.
IN ROOTS, THE APICAL IS LOCATED NEAR THE TIP,
WHERE IT REGENERATES THE ROOT CAP AS PRODUCING
THE PRIMARY MERISTEMS.
THE APICAL MERISTEM OF SHOOT IS LOCATED IN THE
TERMINAL BUD, WHERE IT GIVES RISE, MODULE BY
MODULE, TO A REPETITION OF INTERNODES AND LEAFBEARING NODES.
MODULAR CONSTRUCTION OF A SHOOT
C. SECONDARY GROWTH: LATERAL MERISTEMS ADD GIRTH BY
PRODUCING SECONDARY VASCULAR TISSUE AND PERIDERM
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THE VASCULAR CAMBIUM DEVELOPS
FROM PARENCHYMA CELLS INTO A
MERISTEMATIC CYLINDER THAT
PRODUCES SECONDARY XYLEM AND
SECONDARY PHLOEM.
THE CORK CAMBIUM GIVES RISE TO THE
SECONDARY PLANT BODY'S PROTECTIVE
COVERING, OR PERIDERM, WHICH
CONSISTS OF THE CORK CAMBIUM PLUS
THE LAYERS OF CORK CELLS IT
PRODUCES.
SECONDARY GROWTH OF A STEM
BARK IS PERIDERM PLUS SECONDARY PHLOEM-ALL THE
TISSUES EXTERNAL TO THE VASCULAR CAMBIUM.
A SUMMARY OF PRIMARY AND SECONDARY
GROWTH IN A WOODY STEM