Seed Dispersal refers to mobility of seeds from one place to another by several ways. It plays significant role in establishing the species in a new area. It is a miracle that nature has provided seeds with ideal qualities for this phenomenon to occur. Once seeds get detached from its parent plant, it disperses to considerable distances via external agencies, still retaining their viability for long periods. Moreover, withstand the hazards of environment up-to a large extent.
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Seed Dispersal (Reproductive Biology of Angiosperms)
1. Submitted to: Prof. Sarvarinder Ma’am.
Submitted by: Mohit Sharma
Class: M.Sc Botany (Semester-II)
Paper-IX: Embryology of Angiosperms
Roll No. 763
2. What is Seed Dispersal?
What are the biological significances/implications of this
phenomenon?
What are the various modes by which seeds are dispersed/carried
away to various locations?
Elucidate briefly upon:
(a.) Autochory.
(b.) Anemochory.
(c.) Hydrochory.
(d.) Zoochory.
Surprise.
3. What is seed dispersal?
Adaptive mechanism or phenomenon.
Mainly responsible for its participation in the movement or
dissemination of seeds away from their parent plant.
Ensures the germination & survival of some of the seeds to adult
plants.
i.e. Seeds (under action Seedling.
of wind, water &
animal)
4. Biological Significance of Seed Dispersal
If a plant bears numerous seeds & all of them fall & germinate right beneath
the parent plant, the seedlings would compete for light, water & minerals due
to high mortality.
Being grouped at one place they could easily be detected by animals &
destroyed.
Concentration of the individuals of a species at one place would increase
chances of back-crossing &, consequently, poor progeny.
A dense local population of a species is much more vulnerable to epidemic
attack of fungi & insects, & other local catastrophic could lead to complete
extinction of the species.
5. Modes of SEED Dispersal
Based on the agencies involved, seed dispersal may be of two types:
(a.) By plant itself-
Including: (i) Autochory (i.e. Mechanical dispersal).
eg. Dry pods of leguminous plants.
(b.) By external agencies (also referred to as Allochory)-
Including: (i) Anemochory (i.e. Wind dispersal).
eg. Seeds of Gossypium
(ii) Hydrochory (i.e. Water dispersal).
eg. Fruit of Cocos nucifera floating on the surface of water.
(iii) Zoochory (i.e. Dispersal by animal & man).
eg. Spiny & sticky fruits of Achyranthes & Boerhaavia.
6. AUTOCHORY
Derived from Greek word (i.e. Autos = self, chorein = to spread).
It is the self dispersal of seed by the plants itself.
BALLOCHORY: A type of dispersal where the seed is forcefully ejected by explosive
dehiscence of the fruit. Also called as Explosive mechanism.
Given below are few examples with certain exception describing the autochory
(especially ballochory):
(i) In this, expulsion of seeds is brought about by the dessication or
accidental turgidity of the cells of fruit wall with a sudden jerk.
i.e. Impatiens parviflora; seeds are dispersed to a distance of 2.5 m.
(ii) Also occurs due to build-up of internal or high turgor pressure exerted
inside fruit in which mucilage containing seeds are ejected out through
the opening with a great force.
i.e. Squirting cucumber, Ecballium elaterium.
9. AUTOCHORY
(iii) Probably most efficient mechanical seed dispersal is found in
Arceuthobium, in which cells of viscid layer generate a considerably high
hydrostatic pressure & pericarp contracts to hurl the seed with great
force.
The initial velocity in which the seed is hurled has been calculated as
2,600 cm per second (for A. vaginatum & A. americanum).
The maximum distance to which the seeds of A. vaginatum are thrown
by this method is 1,463 cm.
Do you know?
Barochory: A type of autochory in which plant use of gravity for seed dispersal & also
allows for later transmission by animals & water such as Malus domestica & Cocos
nucifera.
11. ANEMOCHORY
Derived from Greek Word (i.e. Anemos= wind, chorein=to spread).
It is the dispersal of seeds through the agency of wind or air currents or storms; thus
regarded as natural means of dispersal of seeds for the plants.
The anemochorous plants usually possess the following adaptive features for the dispersal-
(a.) Minute & light weight seed.
(b.) Winged seeds:
(i) Seed Coat (testa)
(ii) Persistent sepals.
(iii) Pericarp.
(Orchis seed) (Winged Seed)
13. (a.) Minute & Light weight seeds
Light weight, minute and dusty seeds are easily blown away to long distances by air
currents.
e.g. Orchid seeds being so tiny are often called dusty seeds, are said to produce
about seven hundred million seeds per plant.
Do you know?
Seeds of Orchis maculata are smallest in the plant kingdom.
Each seed weighs only 0.004 gm.
They can be carried to over 1000 km by light wind.
14. (b.) Winged Seeds
Seeds develop thin, dry or membranous wing like structures to float in air & carried to long
distance. Wings work like gliders in the air.
(i) Seed Coat (testa):
Wings may be the expansion of the seed coat as in
Cinchona, Oroxylum.
(ii) Pericarp:
Wings may be the expansion in the pericarp
i.e. Maple seeds. (Oroxylum seed)
(iii) Persistent Sepals:
It is seen in Dipterocarpus & Shorea robusta.
15. (Maple seeds) (Shorea seeds)
Fact: Largest wing (up to 10 cm) is found in the seeds of Zanonia macrocarpa,
a tropical cucurbit.
16. (c.) Parachute Mechanism
(i) Pappus:
Hair like structure & modification of calyx.
e.g. Taraxacum officinale & Tridax procumbens.
(ii) Coma:
Seeds develop tufts of hair develops on one or both ends of the seeds.
e.g. Calotropis procera, Alstonia scholaris.
(iii) Hairy Outgrowth:
e.g. Found in Gossypium.
18. (iv) Balloon-like appendages:
Floral parts of some plants become inflated, float in the air & are
carried to long distance.
e.g. Colutea (Swollen ovary), Physalis peruviana (the persistent calyx is inflated),
Cordiospermum halicacabum (pericarp is inflated).
(Physalis peruviana)
19. (d.) Censor Mechanism
The small-sized seeds are dispersed through small openings on the
fruits.
These pores allow only few seeds to disperse at a time when fruits
swings in the air.
e.g. Papaver somniferum (Poppy), Argemone mexicana,
Antirrhinum, Nigella.
20. (e.) Rolling Mechanism
Some annual plants (e.g., Amaranthus album, Chenopodium
album, Salsola, Carthamus oxycantha) dry out after bearing fruits
& seeds.
They get uprooted by wind and roll over the ground, shedding their
seeds on the way.
These rolling plants are collectively called ‘tumble weeds’.
(Amaranthus album) (Chenopodium seeds)
21. HYDROCHORY
Dispersal of seeds by means of water.
Possess devices that prevent the penetration of water into the seeds, and keep them
afloat for long periods.
(i.) Cocos nucifera
- Fruit possess fibrous mesocarp which encloses large air spaces to help
them float in water.
- The outer epicarp is smooth & waxy.
- Due to these adaptations, fruits are carried away to long distances
(about 4,800 km for a period over 110 days) along sea shore.
(ii.) Nelumbo or Nymphaea
- Seeds are small & light, enclosed in an extra layer of cell, leaving a
layer of air spaces in between.
23. ZOOCHORY
It is the dispersal of seed by animal.
It is brought about by two main ways:
(a.) Endozoochory.
(b.) Exozoochory.
Various other modes of seed dispersal are:
Synzoochory, Ornithochory, Myrmechory, Ichthychory,
Chiropterochory, Malacochory, Saurochory &
Anthropochory
24. 1. ENDOZOOCHORY
Endozoochory is generally a coevolved mutualistic
relationship in which a plant surrounds seeds with an
edible, nutritious fruit as a good food for animals that
consume it.
25. 2. EXOZOOCHORY
Seed dispersal by transporting on the outside of
animals - usually on the hair of mammals.
26. 3. SYNZOOCHORY
Synzoochory is dispersal of diaspores by
the mouthparts of animals, & should possess hard skins
to protect seeds from damage of mouthparts; for
example, sharp beaks on animals such as birds
or turtles.
29. Rapid Fire Round
1. Persistent Sepals is seen in:
(a.) Amaranthus. (b.) Shorea (c.) Taraxacum
(d.) Physalis.
2. Which of the following is/are biological significance of Seed
dispersal?
(a.) Disease resistant plants are not obtained.
(b.) Extinction of species.
(c.) Poor progeny.
(d.) Struggle for existence among seedlings.
30. 3. Anthropochory refers to?
4 Censor mechanism is seen is __________.
5. Viscin-like substance is found in ________.
6. Squirting cucumber is also known as _________ & mode of
dispersal in this is _________.
7. Define Barochory?
8. Seed dispersal by transporting on the outside of animals
usually on the hair of mammals are called __________.
9. Which type of seeds are most efficient to carried to long
distances?
10. Which type of seed dispersal is most common?
