Biology 1A Oct 29, 1998
Lecture 17 - Stems & 2° Growth
Page Contents :
Overview of Lecture:
The shoot develops from the shoot apical meristem.
Secondary growth in stems.
Overview of Lab:
(A bullet indicates a handout.)
- Stems & 2° Growth.
I. The shoot develops from the shoot apical meristem.
A. Reprise : Three regions of development
II. Shoot Anatomy.
a. cell division
B. Reprise : Apical meristems give rise to three primary meristems.
b. cell growth
c. cell differentiation
1. The three 1° meristems result directly from the apical meristems.
2.The three 1° meristems give rise to the three 1° tissue systems:
a. protoderm --> epidermis
3. leaf primordia
b. procambium --> vascular tissue
c. ground meristem --> ground tissue
4. bud primordia
A. Overview of tissue system locations
III. Shoot Systems.
C. Ground tissue
D. Vascular cylinder
2. stomata & guard cells
1. stele - refers to the arrangement of the vascular tissue
a. protostele - roots and primitive stems
2. xylem inward, phloem outward
b. siphonostele - ferns
c. eustele - most seed plants, including dicots
d. atactostele - monocots
3. bundle caps and sclerenchyma sheaths
4. lactifers in the phloem
5. Monocot vs. Dicot
A. Shoot system organization
IV. Secondary growth in stems.
1. nodes and internodes
B. Root system vs. Shoot system
2. leaves and axils
3. buds and branch shoots
4. axillary vs. terminal buds
1. The plant is divided into two primary organ systems: root & shoot
C. Stem specializations
2. How do you tell whether a structure is part of the root or shoot?
a. cuticle; stomata
3. For thought: The organization in the root and shoot of a plant are different . . . .
b. nodes and internodes; leaves
c. endodermis & pericycle
d. vascular organization; leaf gaps
e. most roots are exarch; most stems endarch
2. runners and stolons
A. Primary vs. Secondary growth
1. primary increases length; secondary increases girth
B. Properties of secondary meristems
2. 2° growth produces wood and bark
3. 2° growth limited to seed plants (dicots & gymnos) and some other extinct plants; absent in monocots
4. 2° growth can occur in roots as well as stems
1. lateral, not apical
C. Vascular cambium
1. between xylem and phloem
D. Cork cambium
2. secondary xylem (wood) to inside
3. secondary phloem to outside
1. replaces epidermis as tree grows
2. cork to outside, phelloderm to inside
3. cork vs. bark
atactostele eustele shoot system
axil internode siphonostele
axillary bud lactifer spine
bifacial lateral meristem stele
bark leaf gap stolon
bud primordium leaf primordium stomata
bulb node terminal bud
bundle cap pith thorn
cladophyll prickle trichome
cork cambium protostele tuber
corm rhizome vascular cambium
cortex sclerenchyma sheath wood
cuticle secondary growth
- How do stems differ from roots? Consider each of the three tissue systems.
- What are nodes? Where are nodes found? What structures may be attached at nodes?
- What specialized structures and cells may be found in shoot epidermis?
- What is the difference between cortex and pith?
- What is a protostele? siphonostele? eustele? atactostele? What parts of which plants have each?
- What is a bundle sheath and what function does if serve?
- Why are collenchyma and sclerenchyma more common in shoots than roots?
- Where could you find lactifers in a plant? What two possible functions can they serve?
- Diagram and compare the stem of a typical monocot and dicot. Which tissues are found in dicot stems, but not in monocot stems?
- What is a bud? What is the function of a bud? What is the difference between a terminal and axillary bud?
- Describe stem specializations in which the stem grows horizontally. in which the stem is underground. in which it has been modified for storage.
- Explain the difference between thorns, spines, and prickles.
- Explain the difference between primary and secondary growth.
- What are the three primary meristems? What are the two secondary meristems? Where can each meristem be found? What tissues does each meristem produce?
- Can secondary growth occur in roots?
- How is bark formed? How is cork different from bark? Why does girdling a tree by removing the bark all the way around kill the tree?
- What is the function of cork? What chemical makes this possible?
© 1998 Brian R. Speer. These pages for the personal use of students and teachers; any commercial use or publication is strictly prohibited.