Seed adaptations

Question 1

What is seed adaptation

Answer 1

1. Seeds distribute the plant species, and ensure survival over time, especially for short-lived species.
2. For annuals, seed is an alternative to dormancy.
3. Reproduction by seed ensures genetic variation - genes from both parents.
4. Quantity and method of distribution may vary enormously.
5. Seed has many different germination requirements - often it is not to the plant’s advantage to be “easy” to germinate.
6. Seeds need to be stored appropriately, and we must learn the germination requirements.

Question 2

What does dispersal in time mean?

Answer 2

Dispersal in time is the concept that any dormancy mechanism exists to allow
the seed to germinate over longer periods of time, rather than immediately on
reaching maturity.

Question 3

Techniques to overcome dormancy in horticultural situations:

Answer 3

Washing
Scarification
Stratification

Question 4

What is washing?

Answer 4

some seeds (and the flesh around the seed) contain germination inhibitors to prevent vivipary and provide dispersal in time*. Washing can remove these chemicals, (as can the cleaning and removal of flesh from the
seed).

Citrus x limon.

Question 5

Define vivipary

Answer 5

a seed that germinates into a seedling before being shed from the parent plant

Question 6

What is scarification

Answer 6

Some seeds have seedcoats (testa) which inhibit the movement of water or oxygen. These seed coats prevent or limit germination.

Horticulturists either abrade these seed coats or can chip sections of them away to allow the ingress of water and oxygen

Fabaceae family; Lathyrus odoratus

Question 7

What is stratification

Answer 7

Some seeds require a period of cold to trigger the germination process. Horticulturists ensure that this requirement is met by stratifying seeds, for example placing seed in a fridge or freezer

1. Nearly all trees and shrubs
2. Delayed germination
3. Common in cool winter climates

Fraxinus excelsior

Question 8

What is the impact of seed adaptations on biodiversity and garden design

Answer 8

1. seeds, which have high levels of oils and starch as nutrient dense food sources for wildlife
2. cultivation of plants from seed within garden design, for example pictorial meadows.

Question 9

What is The impact of dispersal mechanisms on garden maintenance

Answer 9

1. grassed areas that are biodiverse may have seed heads of Taraxacum officinale, which release seed that can colonise new garden areas.
2. dispersal in time allows for the build-up of seed banks within the soil. This has impact on horticultural maintenance, for example, the development of techniques such as stale seedbed method of weed control

Question 10

List methods of seed adaptations

Answer 10

• quantity of seed produced
• dispersal mechanism
• dormancy mechanisms
• seed coats
• storage of fats and oils
• orthodox
• recalcitrant.

Question 11

What is a dehiscent seed?

Answer 11

Seeds are dry.

if the pericarp splits open at maturity and releases the seeds

Seeds burst on their own when mature.

Example: Legumes and poppies

Question 12

What is a indehiscent seed?

Answer 12

Seeds are dry

if the pericarp remains intact when the fruit is shed from the plant.

Must decompose to disperse seeds.

Fruit/seed combo.

Example: Corylus avellana (hazel) NUTS

Question 13

Dehiscent vs indihescent seed

Answer 13

dehiscent if the pericarp splits open at maturity and releases the seeds, or indehiscent if the pericarp remains intact when the fruit is shed from the plant.

Question 14

What are fleshy seed examples?

Answer 14

Blackcurrant (ribes)
Apples (Malus)

Question 15

List the seed dispersal methods

Answer 15

Wind
Spring loaded
Burrs,
Animals,
Shaking

Question 16

Explain wind dispersal method

Answer 16

Seed with fluff attached to catch the wind and blow away.

Examples Clematis spp and Taraxacum officinale

OR Samara: Seeds with sails to catch the wind (ACER - MAPLES)

Question 17

Explain spring loaded seed dispersal method

Answer 17

as it dries out, will suddenly
snap, this shoots the seed off – up to 1-1.5 metres from the plant.

Geranium sanguineum

Question 18

Explain the Burrs dispersal method.

Answer 18

hooks that are designed to
cling on to animal fur, which can carry the seed very far away from the parent.

Arctium lappa

Question 19

Explain the animal dispersal method

Answer 19

Wrap seed up in something nice, tasty and nutritious,
and some animal will come along and eat it. They will then excrete it possibly some
kilometers away

Rosa canina

Question 20

What is the shaking method of seed dispersal

Answer 20

having a seed pod that
vibrates in the wind and simply scatters the seed, probably only a metre or so from the plant. For many annuals and perennials that is good enough.

Heracleum maximum

Question 21

What are orthodox seeds?

Answer 21

seeds that can be stored dry, in good conditions for several years.

Good conditions means minimum humidity (so best to store in airtight containers,
preferably with a water absorbing material such as silica gel) and at low temperatures.

The seeds that last the longest tend to be those species (like poppies), which can survive in soil buried for many years until that soil is disturbed.

Question 22

Roughly how long do seeds last (seed viability)

Answer 22

Quercus 3 months
Peas 3 years
Lettuce 6 years
Poppies 100 years

Question 23

Define recalcitrant seeds

Answer 23

Seeds that do not last very long. They usually have high levels of oils or water.

As they dry out, they lose viability.

They cannot be frozen; they cannot be dried

EXAMPLE: Quercus and avocadoes

Question 24

How does germination work

Answer 24

Germination is often staggered, needs to be made difficult or needs to be triggered by something that will provide good conditions.

Often the seed coat will contain chemical germination inhibitors that slow down the
germination process

Seedlings face dangers so protect the species from FIRE, WINTER, DROUGHT OR EATEN.

Question 25

What are germination triggers?

Answer 25

Two elements that trigger germination are cold and fire.

Question 26

Explain how germination in cold works?

Answer 26

Going through a cold spell very often triggers germination.

As the seed warms up after that cold spell, it will know spring has arrived and it is safe to grow

Question 27

How does germination work with fire?

Answer 27

Fire clears land of competition and creates a sterile seedbed for plants to grow.

many species in fire prone areas produce seed that
will only germinate after fire when growing conditions are good, you will then have a mass germination after a fire.

Question 28

What is seed dormancy?

Answer 28

seeds that are held back from germination

Cold can produce this effect

Some species which are eaten particularly by birds will only germinate well after they have been through the digestive tract of a bird (can take years to germinate)

Fire (clears area from competition)

Question 29

How do scarification seeds in fire prone areas break dormancy?

Answer 29

SMOKE.

the chemicals in smoke facilitate germination.

Question 30

What is a seed bank?

Answer 30

seed which is buried in the soil. Mostly short lived species.

That seed will very often live for decades. Disturb the soil and the seeds in the seed bank will start to germinate.

Can be an issue and you may need to disturb the soil a few times to get the seeds to germinate and then remove.

Question 31

Why are there differences in behaviour of seed germination?

Answer 31

Related to the life cycle and level to which the plant needs to grow and develop in the first year.

Question 32

What is the difference between annuals and perennials in their behaviour?

Answer 32

ANNUALS: short lived plants. Seeds germinate quickly, uniformly and easily. Usually long lived seed that waits for good condition in soil

Annuals only need to grow a big enough plant to flower an seeds to keep the species going.

EX: Digitalis purpurea

PERENNIALS: Need to lay down reserves and build bigger root system in the first year.

Woody growth is slow, so slow growth and seedlings vulnerable. May be killed by first frost so STAGGERED germination to reduce risk of death.

Some perennials that produce seeds in summer can germinate from fresh seeds and can survive winter.

Question 33

What is the general rule for seed germination

Answer 33

Use fresh seeds, as soon as mature on the plant.

Seeds deteriorate over time.

Question 34

Why do plants have seed dissemination differences?

Answer 34

Varies in how much seed they produce and the size of the seed.

Either vast quantity of small seeds (with little reserves) OR smaller quantity of larger seeds (store considerable quantity of nutrients - better start in life)

Question 35

Why are there different seed heads?

Answer 35

Evolved to disseminate the seed.

Prefer not to stay in one place so spread as well as possible.

Digitalis: seed capsules on tall stems.

Allium: Seed just falls out

Asclepias incarnata: ‘fly away’ seed

Quercus: Large seeds full of reserves for 1st year food source…short lived (3 month viability).

Question 36

How to germinate very hard seeds?

Answer 36

Hard seeds done to slow down and stagger germination as water takes time to penetrate coat.

1. Drop in just boiled water.
2. Chip coast with knife
   Grind with sand paper.

Question 37

Why is it important to use seeds?

Answer 37

1. Reproduction of good plants.
2. Ensures genetic diversity
3. Preserves heritage varieties

Question 38

Why is knowing how seed dispersed is important?

Answer 38

Helps in collection of seed at the right time.

Understanding the appropriate storage for long term preservation

Awareness of plants and survival in the seed bank - important for ground preparation

Self seeding can be attractive (esp. in dynamic ecological schemes - but can be invasive)

Question 39

Inhibitors of seed spread

Answer 39

Heavy mulch
Dense planting

Awareness important to prevent issues like becoming invasive - esp wildland areas.

Question 40

Important factors for seed adaptions

Answer 40

1. Know plant lifecycles and habits.
2. Understand sowing time (esp whether fresh seed or storing)
3. How to break dormancy

Question 41

What are the significant seed adaptations?

Answer 41

Dispersal
Dormancy mechanisms
Range or adaptations and advantages
Benefits of adaptation

Question 42

Name THREE different mechanisms plants have for
dispersal of their seed. Give a named example for each.

Answer 42

a. WIND: Small seeds with fluff to help spread the seeds far and wide. Taraxacum officinale.
b. SPRING MECHANISM: Seeds that suddenly snap disseminating seeds up to 1.5 metres away. Geranium sanguineum
c. BURRS DISPERSAL: Seeds that are designed to cling on to animal fur, which can carry the seed very far away from the parent. Arctium lappa

MODEL:
seed in edible berries, to be eaten and dispersed by birds – rowan, Sorbus
aucuparia

spring mechanism – Geranium phaeum

small seed with fluff to float away on wind – dandelion, Taraxacum officinale

Question 43

Distinguish between stratification and scarification in dealing with seed.

Answer 43

a. STRATIFICATION: The process of pre-treating a seed in order to simulate the natural conditions that would help break dormancy and allow the seed to germinate. An example would be a period of cold, as in putting the seeds in the refrigerator to simulate winter conditions. Example: Fraxinus excelsior
b. SCARIFICATION: The process of opening up the seed for the movement of water or oxygen as the seed coats prevent or limits germination this way. An example would be chipping the seed to allow the water or oxygen to enter the seed and begin germination. Legumes, especially the Fabaceae family and Lathryus odoratus.

MODEL:
These are both ways of dealing with seed which is slow to germinate. In
stratification, the seed is left outside and exposed to all weathers; cool
temperatures will often stimulate germination, or more usually warm, followed
by cool; it can also be done artificially in a refrigerator. Scarification is a
physical process of wearing away part of the seed coat with, for e.g.
sandpaper, to make it easier for water to penetrate and start the germination
process.

Question 44

Distinguish between orthodox and recalcitrant seed. How is each type stored? Give an example of each.

Answer 44

a. ORTHODOX: Seeds that can be dried and stored in a cool environment, usually 5C for many years. Place seeds in a paper bag with silica gel in an airtight container. Most annuals are orthodox seeds. EXAMPLE: Legumes, such as the Fabiaceae family.
b. RECALCITRANT: Recalcitrant seeds have high levels of moisture or oils and cannot be stored for long, and definitely cannot be dried. They can be sown when fresh only. EXAMPLE: Aesculus hippocastanum

MODEL
Orthodox seed is dry, and needs to be stored in cool dry conditions. Very
often it will remain viable for many years, e.g. carrot, Daucus carota.

Recalcitrant seed is moist or oily and cannot be stored long-term. For shortterm storage it needs to be kept cool and moist, e.g. English oak, Quercus
robur

Question 45

If you have been given seed from a range of hardy plants and are not able to find out much about their germination requirements, describe what you would do with them. Most of the seeds are quite large, but some are also very fine. It is late summer.

Answer 45

a. LARGE SEEDS: These seeds store a considerable amount of nutrients to help them through their first year of life.
b. SMALL SEEDS: These seeds will have a minimal amount of nutrient reserves.
c. As most plants need stratification (cold temperatures to germinate) I would plant the large seeds in late summer so they can experience the cold temperatures of winter. This will give them the warm temps of summer, cold temps of winter followed by the warming temps of spring and will break dormancy naturally. They also have a good amount of nutrients to see them through the cold temperatures.
d. Not knowing what the very small seeds are, I would be hesitant to plant them in late summer. They do not have the nutrients to see them through a cold winter. I would most likely sow the seeds in trays, cover them for the natural greenhouse effect and watch them carefully. When they germinate, I will remove the cover and continue to watch carefully. As the seeds may be of a slow growing plant, I would wait up to 2 years and watch carefully. Some plants spend the first year growing roots and the second year grow above ground. After two years, with no results I would feel comfortable discarding them.

MODEL
Many hardy plants need stratification, therefore I would sow most of them
immediately, so that they could experience warm and then cold conditions.
The only ones I would not sow immediately, would be the very small ones, as
these rarely need stratification; these I would sow in spring, as the weather
begins to warm up. I would sow into seed trays, enclose in a clear plastic bag
and leave the seed trays in a lightly shaded place. I would inspect regularly
and twice a week in spring, and take out of the bag as soon as germination is
seen. I would not discard trays of ungerminated seed for two years.

Question 46

What is the ‘Seed Bank’ and what are the implications for both creating new areas in the garden and garden maintenance? What techniques might you use to minimize the problems created by it: both in site preparation, after planting and during subsequent maintenance. But, might there also be advantages to some aspects of the seed bank – particularly for biodiversity?

Answer 46

a. A SEED BANK is the seed buried in the soil which is waiting for the day when conditions are right to germinate.
b. IMPLICATIONS: When creating a new area in the garden, disturbing the soil will bring the seeds to the surface allowing the right conditions for germination. This will produce a plethora of weeds and plants that need to be removed. Hoeing the area will be important and waiting to see if that has produced more weeds. You may need to hoe a few times to remove all the plants that have germinated.
c. Once you have exhausted the weed germination, adding a layer of heavy mulch will help to stop more germination of seeds as the light will be reduced/eliminated by the mulch, usually about 10cm thick.
d. Regarding biodiversity, some weeds are good for pollinators so perhaps accepting some weeds in the garden is a good idea, especially weeds such as Taraxacum officinale. The more variety of plants the better for biodiversity.

MODEL:
The ‘seed bank’ refers to buried seed in the soil, mostly short-lived arable
weeds, which have adapted to survive through seed rather than plants. Seed
remains dormant until the soil is disturbed, light often stimulating germination.
The seed bank creates problems when a new area is developed for planting as
there is often a mass germination of weeds which will compete with the new
plants, sometimes very severely.
Soil can be cleaned of its seed bank if there is time. Soil can be rotovated, and
after germination of weed seeds, the whole area hoed or treated with
herbicide to kill weed seedlings, then rotovated again to a depth of 10cms, the next crop of seedlings removed, and so on until the seed bank is almost
exhausted.
If there is no time to do this, then new plants should be surrounded with a 5-
7cms layer of coarse mulch to suppress weed seed germination, along with
regular weeding.