stems 100926175806-phpapp02
DESCRIPTION
2nd yearTRANSCRIPT
![Page 1: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/1.jpg)
STEMS• Origin• Functions • External Anatomy • Internal Anatomy • Specialized
Stems
![Page 2: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/2.jpg)
Origin
• First stem of a plant develops from part of a seed embryo called epicotyl, w/c is a continuation of the hypocotyl
![Page 3: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/3.jpg)
The Plant Body: StemsFUNCTIONS OF STEMS• Produces & support appendages
of plant (leaves, flowers, fruits) • transport water and solutes
between roots and leaves. • Stems in some plants are
photosynthetic.• Produce & store materials
necessary for life (e.g., water, starch, sugar).
• In some plants, stems have become adapted for specialized functions.
![Page 4: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/4.jpg)
Stems support a display of leaves.
Stems orient the leaves toward the light with minimal overlap among the leaves.
![Page 5: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/5.jpg)
The stem supports a display of flowers
![Page 6: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/6.jpg)
The stem does photosynthesis…
and stores water.
Opuntia-prickly pear
![Page 7: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/7.jpg)
This stem does photosynthesis, stores water, but also produces a defense chemical: mescaline…a hallucinogen.
Lophophora williamsii - peyote
![Page 8: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/8.jpg)
Two Types of Aerial Stems
Herbaceous Stems• Soft & green• Little growth in diameter• Tissues chiefly primary• Chiefly annual• Covered by epidermis• Buds mostly naked
Woody Stems• Tough & not green• Considerable growth in
diameter• Tissues chiefly secondary• Chiefly perennial• Covered by corky bark• Buds chiefly covered by
scales
![Page 9: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/9.jpg)
Herbaceous Stem woody stem
![Page 10: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/10.jpg)
EXTERNAL ANATOMY
![Page 11: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/11.jpg)
![Page 12: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/12.jpg)
STEM APICAL MERISTEM
![Page 13: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/13.jpg)
![Page 14: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/14.jpg)
![Page 15: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/15.jpg)
![Page 16: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/16.jpg)
PRIMARY & SECONDARY GROWTH
![Page 17: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/17.jpg)
Apical DominanceApical dominance refers
to the suppression of growth by hormones produced in the apical meristem.
Lateral branch growth are inhibited near the shoot apex, but less so farther from the tip.
Apical dominance is disrupted in some plants by removing the shoot tip, causing the plant to become bushy.
![Page 18: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/18.jpg)
INTERNAL STEM ANATOMY
![Page 19: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/19.jpg)
Monocotyledonous & Dicotyledonous Flowering Plants
![Page 20: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/20.jpg)
Monocot Stem – cross section
![Page 21: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/21.jpg)
Typical Stem Cross Section (Dicot Stem)
Helianthus annuus-sun flower annual
Pith
A ring of vascular bundles
Epidermis
Cortex
![Page 22: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/22.jpg)
Epidermis - window, reduce water loss
Cortex Collenchyma- extensible support
Cortex Parenchyma- photosynthesis, etc.
Fibers- rigid support
Functional Phloem- conduct sugars etc. away
from leaf to rest of plantVascular Cambium- adds 2° xylem and 2° phloem
Xylem-conduct water and minerals
up from soilPith
-water storage, defense?
![Page 23: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/23.jpg)
VIP Stem: Provide both name and function labels:
outside
to center
Epidermis: reduce evaporation, gas exchange
Cortex: photosynthesis, collenchyma support
Vascular Bundles: conduction
Pith: water storage? defense? disintegrate?
Vascular Bundle:
Phloem Fibers: support
Functional Phloem: conduct CH2O away from leaf
Vascular Cambium: add 2° Xylem and 2° Phloem
Xylem: conduct minerals up from soil
outs
ide
to c
ente
r
![Page 24: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/24.jpg)
Vitis vinifera - grape
![Page 25: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/25.jpg)
Vitis vinifera - grape
Notice how the vascular cambia of adjacent vascular bundles line up side by side.
Notice that cambium tissue differentiates between the bundles, connecting the cambia together.
Remnants of the procambium:Intrafasicular cambium Interfasicular cambium
![Page 26: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/26.jpg)
Vitis vinifera - grapeThe vascular cambium makes 2° tissues:
2° phloem2° xylem
![Page 27: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/27.jpg)
Basswood – 1 & 2 years old
![Page 28: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/28.jpg)
Three years of Secondary Growth
Tilia - basswood
SecondaryXylem
Secondary Phloemcambium
![Page 29: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/29.jpg)
A cork cambium differentiates and produces a periderm.
Epidermis
Cork Cambium
Phelloderm
cutin
suberin
Cork Cells
![Page 30: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/30.jpg)
Over time, the epidermis dies.
The cork cells build up to for a thick layer for the bark of a tree. We use this to make stoppers for wine bottles and so on.
When suberin is fully developed, the cortex cells will eventually be in the dark. So these chloroplasts will lose their function!
![Page 31: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/31.jpg)
Bark =
epidermis + periderm +
cortex + phloem + vascular
cambium
Wood =
secondary xylem only!
Pith =
a small percentage of tree diameter
at maturity
![Page 32: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/32.jpg)
Anatomy of a Woody Stem
![Page 33: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/33.jpg)
Sequoia sempervirens - giant sequoia
The trees pictured below have long lost their epidermis on the woody portion of the stem
![Page 34: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/34.jpg)
The study of the growth rings in wood: Dendrochronology
![Page 35: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/35.jpg)
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).
mid-summer of one year
fall of that yearwinter of that year
spring of the next year
![Page 36: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/36.jpg)
StemsStems—the axes of plants—consist of nodes (where leaves and axillary buds are produced) separated by internodes.
![Page 37: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/37.jpg)
Node - region of the stem where the leaf and bud are borne.
Internode - the part of the stem between two adjacent nodes.
Herbaceous - not woody; dying down at the end of the growing season.
Woody - hard in texture, containing secondary xylem, and persisting more than one growing season.
Acaulescent - having an inconspicuous stem.
Caulescent - having a distinct stem.
![Page 38: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/38.jpg)
Modified & Specialized Stems
![Page 39: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/39.jpg)
Bulbs• Bulbs - large buds
with a small stem at the lower end surrounded by numerous fleshy leaves that store nutrients; adventitious roots at base
• Eg. onion, tulip, hyacinth, daffodil and lily
![Page 40: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/40.jpg)
Corms• Corms - resemble
bulbs but composed entirely of stem tissue surrounded by a few papery scale like leaves, food storage organs with adventitious roots at the base of corms
• Eg. crocus and gladiolus.
![Page 41: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/41.jpg)
Rhizomes
• Rhizomes - horizontal stems that grow below the ground with adventitious roots
• Eg. irises, ferns, and grasses.
![Page 42: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/42.jpg)
Cladophylls
•Cladophylls or cladodes - leaf-like stems modified for photosynthesis
•Eg. butcher's broom, asparagus, orchids (eg. Epidendrum)
![Page 43: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/43.jpg)
Succulent Stems
• Succulent stems - stout fleshy stems that are modified for water and food storage
Eg. cacti
![Page 44: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/44.jpg)
![Page 45: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/45.jpg)
Thorns- for protection from grazing animals
• Bougainvillea
• Honey locust (modified stem)
• Black Locust (modified leaf stipules)
![Page 46: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/46.jpg)
Food Storage StemsPrickly Pear Cactus
Bamboo Shoots Kohlrabi
![Page 47: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/47.jpg)
Food Storage Stems - Sugarcane
![Page 48: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/48.jpg)
Tubers
• Tubers – swollen regions of stems that store food for subsequent growth
• The "eyes" of a potato (irish potatoes Solanum tuberosum) are the nodes of a starch-ladened stem
![Page 49: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/49.jpg)
Stolons
• Stolons or runners - horizontal stem that grow above the ground with long internodes
Eg. Bermuda grass
(Cynodon dactylon)
Spider plant (Chlorophytum)
Fern (Nephrolepis)
Bermuda grass (Cynodon dactylon).
![Page 50: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/50.jpg)
Rosette• Rosette - stem with short internodes and leaves
attached at nodes
![Page 51: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/51.jpg)
Wild Radish – Rosette & BoltWild Radish – Rosette & Bolt
YEAR ONEYEAR ONE YEAR ONEYEAR ONE
A FLOWERING ANNUALA FLOWERING ANNUAL
![Page 52: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/52.jpg)
Common Mullen – Rosette & BoltCommon Mullen – Rosette & Bolt
YEAR ONEYEAR ONE
YEAR TWOYEAR TWO
A FLOWERING BIENNIALA FLOWERING BIENNIAL
![Page 53: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/53.jpg)
Buds
Buds are short embryonic stems. In angiosperms they are found at the nodes, in the leaf axil (the angle formed by the stem and the petiole of the leaf).
Axillary bud - a bud located in the leaf axil.Terminal bud - a bud at the apex of a stem.
![Page 54: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/54.jpg)
PHYSIOLOGY OF STEMS
• Conduction of Materials by Xylem1) Root pressure – powered by transpiration of water from the leaves
2) Transpiration pull and water cohesion – water is pulled up from the roots due to adhesion of water to the xylem walls & tension generated by the water-potential gradient bet. leaves & xylem
Other contributing factors:3) Atmospheric pressure
4) Action of Living cells 5) Imbibition in cell walls of xylem 6) Capillary attraction
![Page 55: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/55.jpg)
PHYSIOLOGY OF STEMS
• Conduction of Materials by Phloem - nutrient-rich fluid in the phloem moves from
areas of high solute concentration & water pressure to areas of low solute concentration & water pressure
• Hypotheses of phloem function are:1) cytoplasmic streaming2) movement through interface3) pressure flow or mass flow
![Page 56: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/56.jpg)
Transpiration-Cohesion Hypothesis for Water Movement
![Page 57: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/57.jpg)
Sugar Loading of Phloem and Bulk Flow
![Page 58: Stems 100926175806-phpapp02](https://reader033.vdocuments.us/reader033/viewer/2022061117/546817d2af7959925f8b5d82/html5/thumbnails/58.jpg)
Sugar Loading of Phloem and Bulk Flow