Specialized Roots and Stems Text Pages: 561

Home , Bulb, Corm, Rhizome

Specialized Roots and Stems Text Pages: 561 – 587.

Objectives:

1. Be able to describe the various types of specialized roots or stems on some species of plants.

2. Be able to describe and explain propagation procedures used to multiply plants by specialized roots or stems.

3. Be able to describe and explain limitations of propagating plants by specialized roots or stems.

4. Be able to predict how physical manipulations or treatments affect propagation of specialized roots or stems.

I. SPECIALIZED STEMS AND ROOTS

A. Introduction – specialized structures

B. Tubers

1. Tuber - is a swollen, modified stem that functions

a. A tuber has all the parts of a stem, and

i. a tuber has buds, leaf scars, and

ii. eyes - are the buds on

iii. a terminal bud is at

iv. tubers exhibit apical dominance

b. The tuber is borne on

c. Examples: 58

2. The growth pattern is that the tuber forms the first year,

a. The tuber is used as a food source and

b. Certain environmental conditions favor

3. Propagate tubers by

4. Tubercles - are small tubers

C. Tuberous Roots and Stems - these structures are

1. Tuberous root - is an enlarged

a. It is a root

b. Buds that are formed are

c. Example:

d. Growth is as a biennial

i. tuberous root forms one year

ii. then in spring, new shoots grow and produce

iii. the swollen root provides

2. Tuberous stems - include swelling of the hypocotyl, lower epicotyl, and upper

a. Note: this structure is vertically oriented

b. More then one bud can be produced

c. Examples:

d. A tuberous stem is perennial

3. Propagation of these specialized roots and stems is by

D. Rhizome - is another type of

1. Rhizome is defined as a specialized stem that is the main axis of the plant, and

a. A rhizome has nodes and internodes that can be

b. Two basic types of rhizomes:

i. pachymorph - is a rhizome that is

aa. it has a compressed, squatty appearance

bb. examples:

ii. leptomorph - has very long, slender appearance and

aa. examples:

2. Growth pattern of pachymorph rhizomes:

a. This type of rhizome appears as a

b. It has determinate growth meaning each clump ends

c. Older sections of rhizomes

d. Roots usually grow on

e. Since vegetative growth, meaning lateral shoots and rhizome production, as well as flower buds form after flowering, all foliage

3. Growth pattern of leptomorph rhizomes:

a. The rhizome is symmetrical and

b. Most lateral buds on the "stem" remain dormant

4. Propagation of rhizomes is

a. Plants are divided before growth starts in

b. Each rhizome piece should contain a

E. Bulbs

1. Bulb - is a specialized underground organ made of a short, vertical stem

a. Vertical stem axis

i. it is fleshy or

ii. it bears a growing point

b. Bulbs scales are fleshy,

i. outer scales store food

ii. inner scales are

2. Bulblets - are new bulbs that form

a. Consider these meristems as new growing

b. Bulblets must be grown to a certain size before

3. Two types of bulbs are

4. Tunicate Bulb

a. This bulb has its outer scales covered by

b. Scales are continuous in

c. Examples:

d. Growth pattern includes vegetative growth first,

i. in the vegetative stage, the bulb must grow to

ii. the developing bulb gains most of its size 62

iii. bulbs go dormant in

5. Nontunicate (scaly) bulbs:

a. This bulb consists of separate scales

b. These bulbs also lack a

i. these bulbs are less tolerant of

ii. nontunicate bulbs must be kept

c. Many species of these bulbs have

i. contractile roots are

ii. these roots shorten and pull the bulb down

d. Example:

e. On some lily species, new bulbs form in the leaf axis on the stem

i. bulblets form

ii. bulbils form on

f. Growth pattern

6. Propagation of Bulbs

a. Offsets - sufficiently rapid method for

b. Bulblet formation on stems

c. Bulblet formation on scales

i. scaling

ii. adventitious bulblets form

d. Basal cuttage

e. Bulb cuttings

F. Corms

1. Corm is a swollen base of a stem and is enclosed

a. Note: corms lack

b. Since a corm is a stem, it has

c. Corms have two types of roots:

i. fibrous roots develop from

ii. contractile roots - are thick or fleshy roots

2. Growth pattern

a. As the stem growth emerges from the corm, the base of

i. this swelling eventually forms

ii. this year's corm deteriorates

b. The new corm puts out stolon-like structures that

i. these small corms are called

ii. cormels develop between

3. Propagation of corms includes:

a. New corms –

b. Cormels –

c. Corm cuttings –

G. Summary

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