1. Chapter 22 Plant Structure and Function: Stems

2. Plant Stems

3. Stem Parts and Functions
Overview of Stems
1. Stem Functions
2. Stem Growth
3. Types of Stem Tissue
4. Parts of the Stem
Interior
Exterior
5. Modifications of the Stem
Above-ground modifications
Below-ground modifications

4. Overview – Classifications by Life Cycle
Annuals One growing season Biennials Two growing seasons Perennials Many growing seasons

5. 3 Important Stem Functions
Produce leaves, branches, and flowers
Hold leaves up to the sun
Transport substances from root to leaf and leaf to root

6. STEM GROWTH Two Types of Growth Primary Growth Secondary Growth
They can grow above ground and below ground depending on the type of plant

7. Trunk: Primary Growth Primary Growth is primarily vertical.
This kind of growth gives the plant its height.

8. Trunk: Secondary Growth Secondary growth is seen in woody plants.
This kind of growth produces stronger, thicker stems from the vascular cambium and cork cambium.
Horizontal Growth

9. Types of Stem Tissue Two types:
Monocot – has vascular bundles that contain the xylem & phloem scattered randomly
Dicot – have vascular bundles that contain the xylem & phloem organized in a ring like pattern

10. Monocots and Dicots

11. Parts of the Stem

12. Inside Stems Vascular cambium Cork cambium
Thin cylinder of tissue that runs length of roots and stems
Cork cambium
Produces cells that develop tough cell walls
Form protective outside layers on stem and roots
Outer bark on a tree

13. Lateral Meristems

14. Parts of the Stem

15. Inside Stems Pith Xylem Spongy tissue in the center
Gets compressed and squeezed as tree grows in diameter
Xylem
Transports substances away from the roots
Roots throughout to the leaves
Osmosis pressure
Sapwood - active
Heartwood – inactive

17. Inside Stems Cambium Layer of cells between the xylem and phloem
Adds growth to the diameter of the tree
Tree rings

18. Three years of Secondary Growth
Tilia - basswood
Secondary
Phloem
cambium
Secondary
Xylem

19. Each year the cambium produces a layer of secondary xylem and a layer of secondary phloem.
This photo shows secondary xylem from parts of three years in Pinus strobus (white pine).
spring of the next year
winter of that year
fall of that year
mid-summer of one year

20. Inside Stems
Phloem
Transports dissolved sugars and other organic compounds throughout the plant.
Transports both ways
Leaves to roots
Roots to leaves

21. Phloem

23. Inside Stems Cork Cambium and Cork (outer bark)
These cells fill up with waxy substance
Waterproofing layer
Die and become outer layer of bark
Don’t stretch – split and peel away
Protect from disease. Insects and dehydration

24. Bark =
epidermis + phloem + vascular cambium
Wood =
secondary xylem only!
Pith =
a small percentage of tree diameter at maturity

27. This tree is Pinus aristata (bristlecone pine).
One individual of this species shows more than 5000 growth rings!
Inner wood, harvested by boring, was used to validate carbon-14 dating.
Imagine the stories that this California tree could tell…perhaps something of migration of Asian peoples down the western coast of North America! They were contemporaries of Pharaohs!

28. Nodes and Internodes Stems care divided into internodes.
At each end of an internode is a node.
A node is a structure on a stem at which two or more leaves are attached

30. Internodes Located between mature tissues Base of nodes in grass stems
Rice, corn, sugar cane

32. Shrubs vs. Trees
Shrubs: Branch from or near base (usually multi-stemmed)
Trees: Branch from well-defined trunk (usually single-stemmed)

33. Above Ground Stem Modifications
Stolons (Runner)
Spider plant, strawberry plant
Horizontal stem that runs along the surface of soil
Asexual reproduction

34. Above Ground Stem Modifications
Crowns
Very short stem at surface of soil

35. Stem modifications
rhizome
corm
tubers
bulb
03_Stems_PPT

36. Below Ground Stem Modifications
Rhizome
Underground horizontal stems
Iris, ferns
Food storage
Asexual reproduction
Bulb
Shortened compressed stem surrounded by fleshy leaves
Narcissus, onion, tulip, tiger lily

37. Below Ground Stem Modifications
Corm
Mostly stem tissue with some scaly leaves at top
Crocus,
Food storage
Tubor
White potato
Swollen underground stem