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BIOLOGY 1411: General Botany
Student Notes
Roots
I
...
Root Functions

III
...
Root Apex
- the apex is where the root grows
- Near the tip is where new cells are made and
recently made cells elongate the root
- This growth in length by cell number and cell
length is how the root makes its way through soil and
find untapped minerals and water

may

- The expanded network of roots provides better
anchorage too
- So a discussion of roots generally needs to
with the apical growth of roots

start

B
...
Zone of Cell Division
- just under the root cap is sometimes a pad of cells, the quiescent center
- May be absent in some species
- However just proximal to the root cap is a a zone of cells that are actively dividing
- We call this the zone of mitosis
- The actively dividing cells are called meristematic cells

D
...
Zone of Maturation
- as we continue to move away from the root rtip, the zone of elongation includes more and more
cells achieving mature states
- Zone of maturation
- Obviously the elongation and maturation zones overlap considerably
- The cells elongate and differentiate
- Cells become mature
- Cells begin to assume their functional roles
- We can distinguish developing different cell types
- These cells are much older than those closer to the apex
- Epidermal cells a few millimeters or perhaps even centimeters away from the root cap are
growing out among the soil particles as root hairs
- These root hairs are quite numerous and greatly increase the surface area of a root
- Increased absorption of:
- Water
- Dissolved minerals

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IV
...


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V
...


Epidermis
Root Hair

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VI
...
Dicot Roots

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VII
...
Stems

Roots
Central area of ground tissue for storage

Stems

VIII
...
Taproot System
- Main root of primary- root system
- Grows vertically downward
- From the taproot arise smaller lateral roots (secondary roots), which in turn produce even
smaller lateral roots (tertiary roots)
- Most dicots produce taproots
- Look at mesquites

B
...
the opposite of a taproot system
- Formed by thin, moderately branching roots growing from the stem
- A fibrous root system is typical of monocots

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IX
...
Storage Roots
- Long-term storage of carbohydrates
- carbs stored in the roots are used to produce the new shoot in the spring
B
...
Prop Roots
- are adventitious roots modified from aerial support
- In many tropical rain forest trees, large woody prop roots develop from adventitious roots on
horizontal branches and provide additional anchorage and support

D
...
Pneumatophores
- are aerial roots modified for gas exchange

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- Provide a pathway for oxygen to get to the cells of the roots growing in the mud of the marshes
and swamps

X
...
Mycorrhizae
- roots of most plant species form symbiotic relationships with soil fungi
- This type of relationship is beneficial to both the plant and the fungus
- Plant benefits from increased surface area for absorption of water and disavowed
minerals
- May also be some protection against pathogens
- Fungi benefits from carbohydrates produced by the plant

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B
...
Not So Symbiotic Relationships

A
...
Strangler Fig
- while young strangler figs from as epiphytes on a host tree
- Birds eat the seeds of strangler figs and posit the seed on the branches of other trees
- Seed germinate and roots cling to the bark of the host tree for months and, in some species,
years have no contact with the soil

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