Seed plants produce vast numbers
of seeds and fruits. Many of these seeds perish due to intense competition,
with some outcompeting others despite their widespread dispersal. Imagine if
they fell directly under the parent plant and their seedlings grew alongside
each other. They would undoubtedly consume the essential nutrients in the soil
and compete for space, light, and air. Such an arrangement would lead to the
environment failing to meet their identical needs, resulting in the death of
all the plants. Furthermore, they would become easy prey for herbivores.
To ensure the survival of plants
and prevent their extinction, Allah (God) Almighty has provided them with
special mechanisms that enable them to disperse widely, thus preventing
competition for soil resources and other environmental resources. Consequently,
they remain to provide us with the food, clothing, fuel, and other necessities
we require. Seeds and fruits are dispersed through various means, which we will
discuss below.
Fruits and seeds are dispersed by
wind using various adaptations, such as the "parachute" structures on
dandelions and milkweed, the "winged" seeds of maples and ashes, and
the fluffy fibers of cottonwood and willow. These features allow seeds and
fruits to travel long distances and increase their chances of finding a
suitable place to germinate, as seen in plants like grasses, pines, and orchids.
Parachutes: Many plants, such as dandelions and
thistles, have fluffy, hair-like structures called "pappus" that act
as parachutes to catch the wind.
Helicopters: Maple trees have a winged fruit
called a samara that spins like a helicopter as it falls, allowing it to travel
farther from the parent tree.
Cottony seeds: Cottonwood and willow trees have
seeds covered in fluffy fibers that help them float on the wind.
Winged seeds: Other trees, like birches and elms,
have seeds with wings that allow them to glide through the air.
Tumbleweeds: Some plants, like the steppe plant Colutea arborea, are dispersed as entire, wind-blown tumbleweeds.
- How wind dispersal benefits plants
Spreading seeds away from the parent plant helps them avoid competition for resources like sunlight and water. They can also reduce the risk of predators and pathogens that may target seeds concentrated around the parent plant. additionaly, they zation: Wind dispersal enables plants to colonize new areas and re-establish themselves after disturbances like wildfires.
Types of winged seeds include Helicopters. These are associated with maple trees, have two-winged seeds that spin as they fall, like a helicopter. Examples include red, silver, and Norway maples. Single-winged spinners have a single, elongated wing and include seeds from ash and some types of maple, like box elder. Asymmetrical seeds often spin as they fall. Double-winged samaras have double wings seeds. joined together at the base, forming a "helicopter" structure. Circular or round-winged seeds have a wing that encircles the seed, sometimes called a "spinning jenny", like elm seeds. Some plants, like the Sal tree, can have seeds with multiple wings, sometimes all similar in length, or a pattern of alternating large and small wings. finally, Gliding seeds have a symmetrical, flat wing structure that allows them to glide rather than spin. Examples include the Bignoniaceae family, like the Jacaranda, and the flying cucurbit. ).
- Pubescens" Fruits
The calyx in many members of the
Asteraceae family is modified into hair-like structures known as down that
remain attached to the fruit after it ripens (Figure 2a). If the fruit detaches
from the parent plant, the downy covering enables it to be dispersed by the
wind from one place to another.
The fruits of some plants, such as
poppies, squills, and arum, open. However, their seeds do not scatter from the
fruit far from the parent plant unless the wind hovers over them.
-Hairs
The seeds of Calotropis procera,
Asclepias, Alitonia, and cotton are surrounded by hairs that cover the entire
body. These hairs may be present at one or both poles of the seed. They aid in
seed dispersal by the wind (Figure 2b:d).
- Perennial Styles
The feathery style of the fruits
of Clematis and Narravalia plants is persistent, which helps the fruits to be
dispersed by the wind over long distances (Figure 3a-b).
This type of fruit and seed is
characterized by its lightness and small size, allowing any breeze to carry it
far from the parent plant. Among these seeds are those of orchids, which are
considered the smallest seeds in the plant kingdom. The fruit of the orchid
contains millions of seeds resembling dust particles. Other seeds characterized
by their small size include those of some grasses. Eucalyptus seeds are also
distinguished by their small size and light weight, in addition to their membranous
wing (Figure 1b). It is worth noting that one gram of eucalyptus seeds contains
approximately 2500 seeds.
Dispersal of Fruits and Seeds by
Water
God Almighty has endowed seeds
that are dispersed by water with fibrous or spongy outer coverings that enable
them to float on the water's surface. This is the case with the coconut, which
is characterized by its fibrous outer covering that carries it across the sea
for long distances without damage. The fruit of the bear coconut (Lotoicea) is
also characterized by this characteristic. The fruit of the Maldivia plant has
a fibrous outer covering. It's worth noting that this fruit weighs
approximately 18 kilograms, and sometimes even more. It can reach a length of
about one meter and takes 6-12 years to mature (Figure 4). In the lotus plant,
the spongy receptacle of the flower supports the fruit on the top of its
hemisphere, allowing it to float on the water's surface, carried by currents or
winds. Seeds, on the other hand, can be small and light, possessing the ability
to float on water. For example, the seeds of the water lily have an outer
covering known as peat (an outer covering for some seeds), filled with air.
Seed Dispersal by Fruit Explosion
Seeds are dispersed from some
fruits by an explosion accompanied by a violent tremor (Figure 5a). This plant
provides one of the most remarkable and fascinating examples of fruit
explosion. Its fruits burst violently, scattering seeds in all directions. The
explosion is accompanied by a very loud sound. Furthermore, many plants
belonging to the Acanthaceae family have been observed to burst their fruits in
dry or wet conditions. They open from the top to the base, forcefully ejecting
the seeds. In many of these cases, the seeds are equipped with curved hooks
that straighten suddenly, helping to propel them far. Thus, when the fruits of Ruellia
[wild petunia] come into contact with water (Figure 5b) after a shower, they
suddenly burst into two valves. The explosion is accompanied by an audible
sound, scattering the seeds in all directions. Similarly, the fruits of the
mature "Barleria" plant burst suddenly when the air is dry,
ejecting the seeds. The fruits of Phlox and Barleria plants burst on sunny
days. The explosion is accompanied by an audible sound, the cracking of the
bursting fruit. Dispersal of fruits and seeds by animals
Many seeds and fruits are
dispersed by animals and humans.
These seeds and fruits are
characterized by special mechanisms that enable them to be easily transported
by humans and animals.
- Hook-like Fruits
Many fruits have surfaces covered
with hooks, thorns, barbs, or stiff hairs, etc. These enable them to adhere to
the bodies of animals covered with wool, fur, or hair. They also allow them to
adhere to human clothing. Often, humans and animals unknowingly carry them to
distant places. Some seeds are covered with thorns and hooks, such as the seeds
of burdock, cocklebur, and beggar's-ticks (Bidens), while the grapple plant
(Devil's Claw) (Figures A-B). Others are covered with clusters of stiff hairs
pointing outwards, such as Burdock (Arctium spp.),
Cocklebur (Xanthium spp.), Burcucumber (Sicyos angulatus), Buffelgrass
(Cenchrus ciliaris), Queen Anne's Lace (Daucus carota)(Figures 6C-D). Still
others bear star-shaped barbs spreading outwards, such as Burdock, Beggar's
Ticks (Bidens), or Cocklebur (Xanthium) (Figure 7B). Some seeds are equipped
with two hard, curved, and pointed hooks, such as the seeds of Martynia
(Tiger's Claw/Cat's Claw), known for having exactly two prominent hooks, or Xanthium
(Cocklebur) and Urena, (Figure 7C), while others bear hard, sharp spines, such
as the fruits of the Tribulus plant (Puncture vine).
- Sticky Fruits:
God Almighty has endowed the
fruits of some plants with sticky glands that enable them to adhere to the
bodies of animals, thus transporting them to distant places. Examples of such
fruits include those of the Boerhavia plant (Figure 7A) and the Plumbago plant.
The seeds of the Viscum plant also possess sticky glands.
Pulp-like Fruits:
Pulp-like fruits are distinguished
by their beauty and vibrant colors, which encourages people to carry them from
place to place to enjoy their aesthetic appeal. Pulp-like fruits are those with
soft, fleshy, juicy interiors, like mangoes, peaches, guava, passion fruit,
persimmons, and berries, used extensively in juices, smoothies, yogurts, and
desserts, with categories including tropical (mango, passion fruit), orchard
(peach, pear), and berries (strawberry, blueberry). These fruits provide
flavor, nutrients, and texture, often processed into purees, concentrates, or
dried forms, with some (like breadfruit or tamarind) even fermented for
preservation
- Edible Fruits:
Birds and humans are important
agents in seed dispersal. Birds feed on the pulp of guava, fig, and grape
fruits, etc. They swallow the seeds, whose embryos, covered by protective
coverings that vary in nature from plant to plant, are unaffected by digestive
juices. These seeds are then excreted with animal feces, which are used as
fertilizer. Humans, on the other hand, transport seeds from place to place for
use in industry and agriculture. Citrus fruits were introduced to Spain, and
corn was introduced to the Old World after the discovery of America. Sugarcane
and cotton were also introduced to North Africa.
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