Plant Form and Function
Today’s topics: • The Plant body • Modular structure • Indeterminate growth • Meristems • Organization of stems and roots – Xylem and Phloem • Secondary growth
11 March 2013
Repeating modules: Stem, Leaf, Bud Indeterminate Growth
http://www.uwgb.edu/biodiversity/herbarium/trees/node_internode01web_gf.jpg
http://learnplantsnow.com/wp-content/uploads/2008/05/2-bud-1.jpg
All Cells of the Plant Body Originate in a Meristem
1 Pattern of cell division affects form Shoot apical meristem Primary Shoot
Young Growth leaf
Developing vascular strand
(a) Planes of cell division
Developing guard cells Axillary bud meristems Unspecialized Guard cell epidermal cell “mother cell” (b) Asymmetrical cell division 0.25 mm
Phloem Xylem Stem x.s. Vascular Tissue Sclerenchyma Ground tissue Vessel Tracheids 100 !m (fiber cells) connecting pith to cortex
Pith Pits
Key to labels
Epidermis Cortex Dermal Vascular Vessel bundle Ground element 1 mm Vascular (a) Cross section of stem with vascular bundles forming Vessel elements, with a ring (typical of eudicots) perforated end walls Tracheids
Fig. 35-19a1 (a) Primary and secondary growth in a two-year-old stem Primary xylem Vascular cambium Secondary Growth Epidermis Primary phloem Cortex Primary phloem Vascular cambium Primary xylem Pith
2 Fig. 35-19a2 (a) Primary and secondary growth (a) Primary and secondary growth in a two-year-old stem Primary xylem in a two-year-old stem Primary xylem Vascular cambium Vascular cambium Primary phloem Primary phloem
Primary phloem Primary phloem Vascular cambium Vascular cambium
Vascular ray Primary xylem Growth Primary xylem Growth Secondary xylem Secondary xylem Secondary phloem Secondary phloem First cork cambium Cork
Periderm (mainly Periderm (mainly cork cambia cork cambia and cork) and cork)
Secondary phloem Secondary phloem Bark
Layers of periderm Secondary Secondary xylem xylem
Fig. 35-19
Annual Rings Vascular Secondary Secondary cambium phloem C xylem
X C
X C P
X X C P After one year After two years of growth of growth X X C P P
Vascular cambium Growth
The Vascular Cambium always produces • Xylem toward the inside • Phloem toward the outside
Fig. 36-3
24 32 42 29 40 Spiral Growth of Shoots 16 11 19 21 27 34 8 3 6 13 14 26 Shoot 1 5 apical 22 meristem 9 18 Buds 10 4 2 31 17 7 12 23 15 20 25 28 Why? How? 1 mm
3 Roots Roots
Roots Cortex Vascular cylinder Root Cross Section Epidermis Epidermis Key Key to labels to labels Zone of Cortex Root hair differentiation Dermal Dermal
Ground Endodermis Ground
Vascular Vascular Vascular cylinder
Zone of Pericycle elongation
Apical Xylem meristem Zone of cell division 100 !m Phloem Root cap (a) Root with xylem and phloem in the center (typical of eudicots)
100 !m
4