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VASCULAR PLANTS
ROOTS
-3 main functions
1. anchor plants in the ground
2. absorb water and water soluble substances
3. transport water and minerals upwards to other parts of the plant.
-Other uses
4. storage of food material made in leaves and stem  sink
TYPES OF ROOTS
- first structure that comes out of the seed is the primary root = main root system
- from it you have secondary roots.
-These roots are arranged in 2 main types
1. taproot system here primary root remains the main root and is the largest.
-grows deep and is very hard to pull out
-plants with a taproot system can survive drought very well.
Examples: dandelions, oak trees.
2. Fibrous root system
- shallow mass of tangled roots that spread throughout a large area
- secondary roots are just as large as primary roots
Examples: grasses, corn, wheat
-
These two (1 and 2) = the main root systems but there are some types of roots
1. Adventitious roots
- are those arising from any plant part other than the seedling root and its branches
- grow from stems or leaves* ( leaf and stem propagation cuttings)
Examples: climbing roots of ivy
2. Prop roots – e.g. corn. These roots grow from stem into the soil = adventitious roots that
grow downwards.
3. Aerial roots
- found in plants that live on trees e.g. orchids, or Spanish moss
- absorb moisture from the air.
HOW ROOTS GROW
Root system can extend for many meters. But growth is only on the root tips.
 The growing tip has 3 distinct growth regions:
Meristematic region
Elongation region
Maturation region
Two regions contribute to increase in root length:
1) Meristematic region  continual cell division. This region is protected by the root cap.
The new cells of meristematic region help to push the root cap through abrasive soil.
2) Cells of elongation region increase in length forcing the root cap and meristem further into
the soil.
Maturation region – cells begin to differentiate  unspecialized cells develop to specialized
cell types i.e.:
 Vascular tissue form inside the root
 Epidermal tissue form outside
 Specialized epidermal cells form extensions called Root hairs. Root hairs increase the
surface area for absorption of water and minerals. The root hairs further from the root tip fall
off.
STRUCTURE AND FUCTION OF ROOTS
The cross section of the root in the maturation region grows into 3 concentric layers:
 Epidermis
 Cortex
 The vascular cylinder
EPIDERMIS
 Single layer of cells surround the root
 Protects the root from bacteria and fungi
 Cells have root hairs for absorption of water and minerals.
CORTEX
 Most of it is composed of parenchyma tissue
 Intercellular spaces permit water top move freely between cells.
 Some plant’s parenchyma cells store food in the form of insoluble starch.
 Endodermis = inner most layer
 Waxy material between these cells limit the flow of water into vascular cylinder.
VASCULAR CYLINDER
 Central core of the root
 Has 4 distinct types of tissue
1) Ring of parenchyma cells called pericyle  secondary roots originate from here.
2) Centre – has xylem  transports water and minerals upwards.
3) Phloem tissue  transports food made in the leaves
4) In some roots, vascular cambium develops  responsible for increase in root diameter.
 During a growing season, vascular cambium produces new xylem cells on inner side and new
phloem cells on its outer side.
 Older roots develop second meristematic layer beneath epidermis = cork cambium.
- Forms tough waterproof outer layer.
- Roots with cork cambium cannot absorb water but can conduct water and store food.
STEMS
Most stems are upright except a few (talk about later)
FUNCTION
1. Supports leaves and exposes them to sunlight.
2. Transports materials such as water.
3. Storage sites for plant food.
4. Some plant stems can carry out photosynthesis.
TYPE OF STEMS
- Two types found in angiosperms
1. Herbaceous stems- soft fleshy
2. Woody stems
Herbaceous stems
- Soft fleshy stems
- Green colour indicates main root system is taking place in stems
- Plants die back to ground in winter
Examples: weeds
Grasses
Food plants
There are two types of herbaceous stems:
-dicots and monocots
 Based on whether they have 1or 2 cotyledons
 Also based on arrangement of their vascular bundles.
Herbaceous monocots
- Vascular bundles are scattered throughout a spongy parenchyma tissue called pith.
- Stem surrounded by epidermal cells that produce a waxy waterproof cuticle.
Herbaceous dicots
-Vascular bundles are arranged in a ring
-Epidermis protection (cortex  collenchyma, parenchyma  support)
-Xylem and phloem in vascular bundles are separated by continuous ring of meristematic tissue
called cambium. * No cambium in monocots. This is why there is little increase in stem
diameter.
-Centre contains parenchyma cells called pith
-Stem has chlorophyll  photosynthesis takes place in the stem.
Woody Stems
- Not many monocots one example = palm trees  Vascular.bundles are similar to
herbaceous monocots.
-
Have special thickening meristem located just below apical meristem.
Woody stem is due to thickening of parenchyma cells.
Dicots – Woody stem
External structure
-
Hard but flexible
Terminal bud  tip of stem. Growth takes place in this region.
Lateral buds. Growth also takes place in this region.
Growth
Pattern similar to that of roots
1. meristematic tissue give rise to new cells
2. new cells elongate and cause stem growth
3. later the cells differentiate to form various types of stem tissue.
-
scales protect buds
scales fall off when bud is growing
Points along stem where leaves are formed are called nodes.
Spaces between the nodes = internodes
Lenticels = holes in cork that allow gas exchange.
Internal structure
- Vascular bundles arranged in a ring
- Have cambium ring between xylem and phloem
- Cambium produces new xylem inside, phloem outside.
- New xylem and phloem are produced each year
- New phloem crushes old phloem against out bark
- More xylem produced than phloem. Therefore central part of stem develops a thick core.
This helps support the increasing mass of the tree.
- Xylem = wood
- Xylem vessels formed in spring are thicker than those in summer. This is due to water
supply.
SUMMARY OF STEMS
STEMS
HERBACEOUS STEMS
WOODY STEMS
Herbaceous
monocots
-tulips
-onions
-grasses
(corn, wheat,
rice)
Dicots
-maple
-oak
-beech
Herbaceous
dicots
-carrots
-beans
-peas
-sunflower
-Monocots
-palm trees
-In spring xylem is a lighter band and in summer the xylem is a darker band. The two bands
together make up the annual ring.
-
In trees, the size of the rings can indicate weather conditions, climate changes, drought,
insect infestation and forest fires.
-
Only new xylem transport material this xylem is known as sapwood. Inner old xylem is
known as heartwood and it is there only for support
- heartwood is dark and has industrial value
- outer side = cork cambium forms
1.) cork on outside of stem
2.) parechyman on inside next to phloem
- as stem grows, outer layer dies, forms protective waxy material that protects stem from
diseases and insects and also reduces water loss.
Stem adaptation
- Stolon- modified stem - grows into the air and then curves downwards
- Rhizomes - underground stems, grow horizontally never appear above ground, e.g. Iris
- Potato underground stem
- Corms or bulbs- underground stems
Corms = short, thick fleshy underground stem, later develops leaves---> e.g. Gladiolus
Bulbs- consist of numerous thick fleshy leaves that surround a very small flattened stem
e.g. onions, daffodils.