Biology 1A    Oct 29, 1998
Lecture 17 - Stems & 2° Growth

Page Contents :

• Reading Assignment
• Overview of Lecture
• Overview of Lab
• Lecture Outline
• Vocabulary
• Study Questions
• Related Websites

Stern: Chapter 6

Overview of Lecture:

The shoot develops from the shoot apical meristem.
Shoot anatomy.
Shoot systems.
Secondary growth in stems.

Overview of Lab:

(A bullet indicates a handout.)
• Stems & 2° Growth.

A. Reprise : Three regions of development
a. cell division
b. cell growth
c. cell differentiation
B. Reprise : Apical meristems give rise to three primary meristems.
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
b. procambium --> vascular tissue
c. ground meristem --> ground tissue
3. leaf primordia
4. bud primordia

A. Overview of tissue system locations
B. Epidermis
1. cuticle
2. stomata & guard cells
3. trichomes
4. glands
C. Ground tissue
1. cortex
2. pith
D. Vascular cylinder
1. stele - refers to the arrangement of the vascular tissue
a. protostele - roots and primitive stems
b. siphonostele - ferns
c. eustele - most seed plants, including dicots
d. atactostele - monocots
2. xylem inward, phloem outward
3. bundle caps and sclerenchyma sheaths
4. lactifers in the phloem
5. Monocot vs. Dicot

A. Shoot system organization
1. nodes and internodes
2. leaves and axils
3. buds and branch shoots
4. axillary vs. terminal buds
B. Root system vs. Shoot system
1. The plant is divided into two primary organ systems: root & shoot
2. How do you tell whether a structure is part of the root or shoot?
a. cuticle; stomata
b. nodes and internodes; leaves
c. endodermis & pericycle
d. vascular organization; leaf gaps
e. most roots are exarch; most stems endarch
3. For thought: The organization in the root and shoot of a plant are different . . . .
C. Stem specializations
1. rhizomes
2. runners and stolons
3. tubers
4. bulbs
5. corms
6. cladophylls
7. thorns

A. Primary vs. Secondary growth
1. primary increases length; secondary increases girth
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
B. Properties of secondary meristems
1. lateral, not apical
2. bifacial
C. Vascular cambium
1. between xylem and phloem
2. secondary xylem (wood) to inside
3. secondary phloem to outside
D. Cork cambium
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?

• UCMP - Morphology of Seed Plants