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Botany

Botany

How plants travel? – The ways they use to spread their seeds

Do plants travel for real? Yes! All plants need to travel in order to survive. They have to travel a lot and to great distances in order to spread themselves and make sure that their future generations thrives. They do this by several ways by implementing the best techniques known to them. These techniques are shaped by the climate, landscape, agents that are available to disperse their seeds, a few to mention. Some just use the natural elements like wind and water. Some make pacts with animals, birds and insects and some do it on their own. Here are some unique ways handled by some plants to disperse their seeds. Plants always make the best out of what is available to them!

Bird Cage plantOenothera deltoides

The bird cage plant or Devil’s Lantern is a plant that grows on sandy soils from deserts to beaches. The plant looks like a small bush that is close to the ground.This plant is native to South Western United States and Northern Mexico. It produces attractive white blossoms and when the dry season comes up, the plant has finished it’s reproduction and has produced seeds that are ready for dispersal. During the dry season, the plant dries up and in that process, curls it up to form the so-called “Bird Cage”

Squirting cucumber – Ecballium elaterium

The squirting cucumbers fill their fruits with liquids that get up to a huge pressure and wait with a huge potential. A slightest touch or an accidental bump by a passing by animal is enough to launch the missiles and the seeds get squirted along with a liquid at speeds upto 95 kmph. Each fruit will contain about 20 to 40 seeds in an average. The seeds may be thrown at a maximum distance of 6 meters in all directions! Great pressure indeed!!

Dandelion – Taraxacum officinale

The Dandelion starts as a normal flower. After the fertilization is complete, the petals of the flowers drop leaving just a seed head which seems much like a bud. After the seeds are mature, the magic happens. The seedhead opens up into a wonderful structure that we usually use to blow off in a playful manner! The seedhead opens up as it dries and each seed is equipped with a tiny parachute that enables it to float and fly away even in the slightest breeze. So, now everything is ready, the plant just waits for a wind to spread it’s seeds. A gentle breeze from a little child’s mouth could send these seeds into the and with a lots of happiness for the child and the plant!

Javan Cucumber – Alsomitra macrocarpa

A. macrocarpa is woody climber produce big “flat” seeds with two big gliders attached to them. They are found in the tropical rainforests of Indonesia and the Malay Peninsula. They climb up high in the rainforest trees and produce huge hanging fruits that hang up in the canopy which aids the dispersal of the seeds. The fruits open up at the bottom as the fruits dry, seeds get loose one by one and they are dispersed in wind. They just float effortlessly in the wind and the gliders help them travel great distances and establish its population!

Helicopter Seeds – Anisoptera scaphula

Helicopter seeds are produced by tall trees which reach up to 45 meters. The seeds of this tree have a good advantage of getting dispersed. These seeds are equipped with two wings that rotate like a helicopter blade and come rotating down from the trees. When wind blows, they can be taken far away from the mother trees!

Coconut – Cocos nucifera

As it is very popularly known, coconuts can be found along sandy beaches and sea shores of all tropical regions. The reason for this is the coconut uses the sea water to disperse its seeds! The coconuts travel in the sea currents. They are perfectly adapted to it. Although the seed is huge and heavy, it is covered by a thick mesh of fibres that contain a lot of air which aids the seed to floating in water.

Sea beans – Entada rheedii

Sea Bean is a woody climber of the Fabaceae family which is found throughout the tropical rainforests along the rivers and near the seas. It is found all over Africa, parts of Asia and Australia but not in the American tropics! Their seed coats are thicker and durable so they survive prolonged immersion in the sea water and germinate when they land in suitable spots! They are found along rivers in Tropical forests where the giant pod hangs above water and the pods once mature, drop off as single packets into the water and are eventually carried to the sea. From there, these seeds travel great distances and reach different islands and establish themselves there. An example of such can be seen in the Archipelago of Indonesia and Papua New Guinea.

African Grapple plant – Harpagophytum procumbens

The African Grapple plant uses a more brutal way to disperse its seeds. It grows in sandy and dry places in Northern South Africa, Southern Botswana in the Kalahari region. The fruits of this plant is evolved as a huge claw like structure which is rightly called as “Devil’s Claw”. The plant aims animals that have big soles like Elephants and ostriches. They accidentally step on the plant and the seed gets painfully embedded to the legs and as they take each step and the seed pod breaks releasing seeds as the animals march the desert.

Durian – Durio zibethinus

The Durian is a tropical fruit that looks a lot like the jack fruit. But they both belong to different families Durian – Malvaceae and Jackfruit – Moraceae. Durian is a very smelly fruit that is found in the tropical rain forests and these fruits are a favourite for Orangutan Monkeys. In a Bornean forest, the Orangutans eat the fleshy fruits of a Durian and the tree is littered with rinds and seeds of the tree. The seeds that fall around the tree are the most unfortunate ones as they are shadowed by the parent tree and they will not get a chance to grow into successful trees. The ones that are accidentally swallowed by the Orangutans are the lucky ones and they get the chance to travel distances and if they are lucky enough, they will get to an open space and germinate there to grow into a tree!

 

Wild avocado – Persea americana

Avocados in wild are relatively small while compared to what we see today in super markets! The bird called “Quetzal” is a specialist in dispersing wild avocado seeds. This small bird can swallow an Avocado with its stone and the seeds are later dispersed when the bird excretes. This gives the plant an extra nutrition to get started! The Quetzal is found only in the tropics of Guatemala, Mexico and Central American continent. For the female Quetzals, the fruits are extremely necessary for good reproduction. It seems to help them produce eggs. So, these birds usually nest near avocado trees.

Guanacaste trees – Enterolobium cyclocarpum

The Guanacaste trees grow from Central Mexico to Northern Brazil and Venezuela. The agents of dispersal of these trees were once giant sloths that lived in the region. But when human started to settle there, they were hunted to extinction. Fortunately, the humans brought with them, big animals like cows and horses. They took the place of the Giant Sloths. The seedpods need big mouths to grind and they pass through the intestines and when they are excreted in the faces, they germinate happily and grow into trees. The trees get their name from the “Guanacaste” province of Costa Rica where they are are found in abundance. Humans have also have become fond of these trees and they have been growing this since then.

Brazil nuts – Bertholletia excelsa

The Brazil nuts are found in the tropical rainforests of Brazil as the name goes. They are one of the sources of income for the country! These trees have their contract with an incredibly small animal called “Agouti” disperse their seeds. These small rodents have strong teeth that can gnaw through the tough capsule of the Brazil nuts. Each capsule contain about twenty nuts which is too much for such a small animal. So, they hide the seeds that they cannot eat for future use. But the Agouti is poor in memory and often forgets where it hides the seeds. The seeds that it hides in the ground germinate and grow into trees.

This is just a sample of how plants communicate with their surroundings and they spread themselves to unbelievable distances. It is a fascinating world and it would be fascinating when we dig deeper and get an understating of every plant that is out there! We will explore more about plants in future posts!

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Botany

The Root System

The root system is the most important parts of the plant because, they do several important functions in silence. We never get to see them at all in most cases. We seldom know how majesty they are in their size. The we look at a tree, we just see and think mostly about what is before our eyes – The trunk, the branches, leaves, flowers and fruits. We get greatly distracted by these of course. Most of us won’t think how the roots of the plants would be, what colour would they be, what is the nature of the roots, how deep would they have gone into the soil, what is their relationship with other organisms and other plants around them in the soil, etc. It is a secret part that always hides itself from the outside world. It is there holding the plant, fighting great wars in utter silence, bringing the things the plant needs either on its own or through amazing partnerships with others. Some may even steal food and water from other roots nearby! Come with me as I dig into the and explore a bit about the roots here!

There are two basically types of root system that are common in plants. They are, Tap Roots and Fibrous Roots.

The Tap Root System

The tap root is characterised by a big, strong anchor root that is a primary root for the plant. Several branches arise from the primary root and they are called as secondary roots and the secondary roots further branch to form the tertiary roots. The tertiary roots end up forming root hairs.

 

The taproot is advantageous in several ways. They are very helpful in anchoring the plants firmly to the soil and hence trees with tap roots can withstand storms at ease. They also go deep inside the soil and can help in absorbing ground water. This will be really helpful for the trees while there is a drought. The Tap Root System is a characteristic feature of the dicots.

The Fibrous Root System

The fibrous root system is a tuft of roots that arise from the base of the stem. They start as a taproot from the radicle after germination. The single root is soon replaced with a tuft of fibrous roots as the plant grows. These are characteristics of a monocot plant. The monocots are generally herbs and shrubs. The fibrous root enable them to hover over on the surface and extract the nutrients of the rich top-soil. Hence, they are mostly short lived except for the Palms which live for several years.

 

A root tip can be classified into four regions –

  • Region of Maturation – The region of the root where the root hairs are present and is the mature part of the root. This is the region of the root where the growth has completed.
  • Region of Elongation – The region of the root where the root grows in length. This region contains cells that rapidly elongating length-wise which results in increase of the root length.
  • Region of Meristematic activity – This region is where the precursor (root meristems) cells are present. These cells continuously grow and get differentiated into other mature cells. This is the region of growth producing new cells.
  • Root Cap – It can be seen covering the tip of the roots. The main job of the root cap is to protect the young meristematic cells. It also helps the roots to push against its odds in the soil like small stones.

The above diagram shows different regions of a root

Functions of the Root System

The root system as it is very important part of the plant has several functions. Some of the important functions that the root system perform are –

Holding the plant upright – The roots are the reason why the plants stand upright. They give enough mechanical strength that is required for the plant to stand straight so the shoot could grow in search of light and perform it’s activities normally.

Searching for new resources – The roots are almost on an endless search. They keep growing probing underground in search of water and nutrition. The tap roots of the fig trees are known to grow the longest roots. The Fig trees found on the Echo caves near Ohrigstad, Mpumalanga, South Africa have tap roots that go in search of water that is 400 feet underground inside the caves.

Photo credit: http://rideintobirdland.com

Another example is the lush and dense forests of the Yucatan peninsula. The Yucatan has great expanses of dense forests although there are no running rivers on it’s surface. The secret is underground inside the caves that hold fresh water. This fresh water supports those great forests. There are openings here and there which are called “cenotes”. The cenotes were an important water source for the Mayan people and they considered it sacred and used some of them to offer their sacrifices to their Gods.

The tree roots of the forests of Yucatan reach to the water underground for water.

Storage chambers – They serve as storage organs for the plants and the reserve food is used up by the plant during the unfavorable periods like periods of drought. Potato, tapioca, carrot, beetroot, sweet potatoes are all examples of storage roots. They not only serve as storage organs but also as resurrectors. Sometimes, the whole shoot of the plant can get eaten up by a herbivore. The underground storage however remains intact and the plant regrows from the storage roots and it is there again!

Underground warfare – Several species of plants are known to protect their territory well by defending themselves vigorously. They wage furious wars underground – a silent war – a chemical war! This helps the plant defeat it’s competitors thereby using up all the resources available for itself. The Spotted Knapweed – Centaurea maculosa, native to the Eastern Europe,is an invasive species in the US and a big problem. This plant wages an underground warfare where it roots release a toxin Catechin which inhibits the growth of several native plants and grasses. By doing this, it has invaded and occupied at least 4.5 million acres of land in Montana alone!

Ecologists tried several ways to control this land-hungry plant. They employed different ways like weedicides, bio-pests, sheep grazing but was not able to control this beast. Fortunately ecologists and botanists in Montana later found a plant (native to Montana) that could counter spotted knapweed’s chemical attack. It was the Lupine – Lupinus sericeus which also had a counter chemical attack against the Knapweed’s toxin. The lupins seem to release oxalic acid which not only counters the attack but also helps to protect the other native plants within the range of the Lupins.

Special functions – The roots are modified into special structures in many plants and trees that perform various functions like providing extra support to plants, enabling the plant breathe in swampy regions, help them absorb water and nutrients from the air in epiphytes and from other host plants in parasitic plants. The modifications of roots is so diverse that it deserves a separate post. So, I leave it here for now.

Economic Importance of Roots

  • We consume several storage roots as food items. The roots are all make delicious dishes! Carrots, radishes, turnips, sugar beets, sweet potatoes, tapioca, Yams and much more. All these roots along with great recipes give delicious dishes.
  • The Yam roots produce estrogen which are used in making birth control pills.
  • Several plants store valuable chemicals in their roots which are used in different treatment methods worldwide. Ginseng, Clitoria ternatea, Aconitum, Gentiana lutea are used in medicine.
  • Several Legume species have root nodules which host nitrogen fixing bacteria and are used in agricultural fields as great nitrogen enhancers.
  • The roots hold the soil together and prevent it from erosion by various agents like wind and water. They also prevent landslides when more trees and plants are planted on steep slopes.
  • The plants on desert sand dunes can help stabilize the sand dunes and thereby facilitating desert land reclamation.
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Botany

Arrangement of Leaves on Stem

Arrangement of leaves on a stem is called as Phyllotaxy. There are several methods that plants use to arrange leaves on their stem. It is basically 4 ways as,

Alternate

In this arrangement, leaves are arranged alternatively on the stem with one leaf per node in a straight line.

Opposite

Here, two leaves arise from a single node in opposite fashion.

Spiral

Only one leaf is present per node as in alternate arrangement. But, the leaves are arranged as a spiral which would be visible if you look down at the apex of the stem.

Whorled

Multiple leaves arise from a single node and each nodes are separated by huge internodes.

Other arrangements include Subopposite and Deccusate.

Subopposite

Here, the leaves are arranged in such a fashion that they are neither spaced far enough to be considered as alternate nor exactly opposite enough to consider as opposite.

Deccusate

This is where two leaves arise from a same node (opposite) in each nodes. The pairs are placed in right angles to each other.

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Botany

Types of Compound Leaves

Leaves occur in various arrangements in plants. All plants seem to have leaves on branches to normal folks. We, botanists should see it different though. Many plants have several leaves in a branch which called leaflets and the whole branch is called as a leaf! These are called compound leaves. So basically there are two types of compound leaves in a broader sense. A compound leaf may be either pinnately compound or Palmately compound.

Before actually getting into the topic, one should know what s simple leaf look like. To be simple, a simple leaf will contain only one leaf that is attached to the stem by a petiole. Whereas a compound leaf will have many leaf lets attached to a stem by means of a petiole. The branch that contains the leaflets are called a rachis.

Pinnately compound leaves

These leaves contain leaflets arranged in opposite arrangement on the rachis (the extended petiole). The leaflets may be evenly paired or oddly paired. In the evenly paired pinnate leaves, the leaflets are arranged in an opposite manner and the rachis ends with two leaflets and is called Paripinnate. In oddly paired pinnate leaves, the leaflets are arranged in opposite fashion with a trailing leaf at the anterior end of the rachis and is called imparipinnate.

Paripinnate leaf

Imparipinnate leaf

The leaves may be of three types based on the number of times of pinnation as follows,

Unipinnate

Single leaflets are present on the rachis in opposite fashion.

Example: Azadirachta indica

Bipinnate

When the single leaflets of the unipinnate leaf gets replaced with unipnnate leaves themselves becomes bipinnate leaves.

Example: Mimosa pudica

Tripinnate

When the single leaflets in the unipinnate leaves get replaced with bipinnate leaves, it is called as tripinnate leaves!

Example: Moringa oleifera

 

Mimosa pudica

 

Moringa oleifera

Palmately Compound Leaves

These are a form of compound leaves that appear as a single leaf but appearances may be deceptive! Multiple leaflets arise from a common point that is at the end of the petiole. Based on the number of such leaflets, they are classified as follows,

Unifoliate

These leaves contain a simple leaf blade as a normal leaf with a winged petiole. Examples: Citrus limon, Citrus maxima

Bifoliate

These leaves will contain two leaf blades attached to the petiole at a single point.

Example: Bauhinia Yunnanensis

 

Citrus limon

Bauhinia Yunnanensis

Trifoliate

These appear to be three leaves originating from the anterior end of the petiole.

Example: Clover leaves are mostly trifoliate and rarely quadrifoliate.

Quadrifoliate

Four leaves would be fused to a petiole and appear to be a single leaf.

Example: Oxalis, Marsilea

Clover Leaves

Marsilea crenata

Multifoliate

When more than four leaflets are attached to a petiole to form a single leaf, it is called a multifoliate palmately compound leaf.

Example: Baobab, Umbrella plant.

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Botany

Modifications of Leaves

Plants have changed themselves to adapt to their environment in excellent ways. One of them is the modifications of leaves. The leaves of several plants get modified into different forms based on the plant’s purpose and environment. Let’s have a look at some of these beautiful modifications here,

Spines

In most xerophytes (plants that grow in regions of scarce water) like Opuntia, the leaves are reduced to spines and the

stem is modified into storage parts which store water for the plants. They also become green and take the responsibility of the leaves by performing photosynthesis.

The spines will also be found in plants like Acacia that grow and survive well in drought conditions. They spines help reduce the water loss. Also, they radiate the excess heat from the stems. They are also useful in absorbing droplets of water from the fog.

While in some plants like ocotilla, the petiole gets elongated and the leaflets grow and the end of the petiole and as the plant matures, the leaflets fall off and the petiole remains as a spine.

OpuntiaAcacia

Succulent leaves

Some plants like Aloe vera have managed to grow fleshy leaves that serve serve as a storage parts for water as well as reserve materials. The plants can survive for months without even a single drop of water and may turn brown. But, even if it gets a little amount of water, the entire plant will turn green in days!

Tendrils

In climbers, the leaf of plants would be modified into elongated structures to help the plants climb efficiently. There are 4 types of tendrils as,

  • Leaves may get modified into tendrils as in Pisum sativum where the apical leaves are modified into tendrils.
  • In some plants like Tropaeolum majus, the petioles are elongated and they grasp the nearby plants for support.
  • In plants like Gloriosa superba, The leaf tips get elongated and become tendrils.
  • In some plants like Lathyrus aphaca, the entire leaf gets modified into a tendril and the stipules expand to carry out the function of a leaf.

Pisum sativum
Trapaeolum majus

Lathyrus aphaca

Hooks

Some plants modify their terminal leaflets into hooks that help the climbers to hold onto its substrate. In Bignonia unguis-cati, the terminal leaflets turn into three hooks and help the plant to climb.

 

Swollen petioles

Aquatic plants live Eichhornia, have bulged petioles that are filled with air and help the plants to float on water.

 EichhorniaSalvinia natans

Leaves modified into roots

In Salvinia natans, an Aquatic fern, has three leaves that develop from each node. Two of the three leaves float above the water while the third leaf is submerged and is modified into a root.

Reproductive leaves

Plants like Bryophyllum daigremontianum produce adventitious buds along their leaf margins. These buds develop roots while on the parent plant and as they mature, they fall off the plant and start growing into a new plant when they land on nearby soil.

 

Sheathy leaf bases

Some plants lack true woody stems. For instance, Musa paradisiaca (Banana) plant the leaf base is expanded into a sheath that is rolled over one another in layers as new leaves grow. The sheathy leaf bases combine to form a pseudo stem that supports the plant to stand erect.

Traps

The plants that grow in nitrogen deficient places have modified themselves well to get it. The carnivorous plants like Nepenthes sp., the leaves are modified into a pod which is used to attract insects and other tiny animals to fall inside and digest them. The inner walls secrete digestive enzymes that help digest the insects and extract the nitrogen needed for the plant.

 

In Drosera burmannii, the leaf margins produce sticky substance that is irresistible to the insects and they fall for it. Then, the leaf rolls up to digest the insect.

In Utricularia vulgaris, the plant leaves are modified into bladders that capture small organisms and digest them. As something enters into the bladder, the valve closes and the digestion process begins.

Phyllode

In Acacia auriculiformis, the petioles expand to form Leaf like structures. They carry out the functions of the leaf. The true compound leaves appear in young plants and they fall off as they start growing. The true compound leaves may appear at the time of formation of seeds but they are short lived!

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Botany

Life cycle of Ferns

Ferns are just wonderful plants that we see in our daily lives. They live a secret reproductive life that is not visible to us unless we have a keen observation. This is because, they do not produce bright flowers or attractive fruits as the angiosperms do. They just produce spores under their leaves and use them to reproduce. Lets get deep into the life cycle of ferns now.

The life cycle of ferns has two forms. The beautiful plant body that we see is called the “Sporophyte” which means Spore bearing plant and is the dominant part of the cycle. There is another form called as the “Gametophyte” or the plant body bearing gametes which is very less-lived when compared to the sporophyte.

Sorus

Sorii are arrays of dots present in the under side of the fern leaves. These sorii contain groups of spores. These spores may be protected by a cover of cells like you can see in the image which has umbrella shaped indusium. The Indusium may be cup-shaped in some ferns and absent in some.

Sporangia

The fern sporangia are connected to the base of the leaves by means of a stalk and they are like a capsule with haploid spores inside them. The spores multiply and increase in number inside the sporangia by meiosis. The sporangia contains two types of cells on its lateral sides. They are lip cells and annulus. The lip cells are found on one side and they are delicate and thin walled cells. The annulus is a ring of cells that connects the stalk on one side with the lip cells on the other side. As they mature, these cells get bulged and are prominently visible. These cells are thick walled and rigid. The annulus and lip cells are responsible for the dispersal of spores.

Dispersal of spores

As the spores are fully mature, the annulus begins to dry due to evaporation of water from its cells. This causes the annulus to pull backwards which in turn pulls the lip cells beyond their stress point. As a result, the lip cells are torn apart making way for the spores to disperse. When all the water gets evaporated from the annulus, it can no longer hold the pull as there is no water to hold it back. The annulus then springs back to its original position. This action throws the spores away from the mother plant.

Germination of spores

The spores landed on the moist soil will start germinating readily. The rhizome emerges first and it attaches to the soil firmly. Then, the seed grows into a heart shaped gametophyte or prothallus. The prothallus retains a notch of growing cells in its anterior position called a “notch meristem”. The posterior end produces several rhizoids that fix the plant firmly in the soil and absorbs water and nutrients for the plant. The male sex organs or antheridia are formed at the posterior end of the plant body and the female sex organs or  archegonia are produces at the anterior end of the plant. In some plants, the archegonia are formed first.

The formation of the sex cells determines whether there would be self-fertilisation or cross-fertilisation. A plant may contain both the sex cells or some times only one. When the archegonia are formed first and if flooded by water, it releases a hormone called “antheridiogen” which stimulates the adjacent gametophytes to produce only antheridium thereby enabling cross-fertilisation!

Antheridium

The antheridium or the male sex organ is the one which produces the male gametes or sperms. The antheridium consists of ring cells that form the outer layer around the spermatids and a cap cell that encloses the opening of the antheridium. As the sperms mature inside the antheridium and when the gametophyte is flooded with water, the motile sperm cells are released from the antheridium.

 Archegonium

The archegonia or the female cells are formed at the anterior end of the gametophyte (near the notch). The archegonia are flask shaped structures. These are made up of a vertical canal cell or the neck cell and a swollen botton called the venter. The venter contains the haploid egg cell.

 

Fertilisation

This wonderful process takes place when the gametophyte is flooded with water. The entire reproduction process happens during the rainy season when there will be abundant water available for the gametophytes. As the rain water floods the plant, it gets stimulated to release the sperms and the sperms with flagellae swim across the water. The flooding stimulates archegonia to produce a substance that will attract the sperms towards it. As a sperm swims into the reach of the archegonia’s attractive secretion, it swims straight into the canal cell reaching the egg cell. The haploid nuclei of the

sperms and eggs fuse together to form a diploid zygote.

A fern gametophyte with a young sporophyte growing from it.

The zygote then begins to divide by mitosis. It first produces the rhizome which initially acts as a root and fixes the young plant into the soil. Later, this forms the underground structure called the rhizome of the sporophyte and gives rise to several fronds.

Mature Sporophyte

A mature fern sporophyte!

The zygote then produces new fronds which develop as new leaves. The plant continues to grow into a mature sporophyte. The mature sporophyte consists of three major parts – The rhizome, fronds and sporangia. Thus, the life cycle of ferns consists of two major plant forms – a long-living sporophyte and a short-lived gametophyte. The life cycle of fern starts again!

You could watch this wonderful YouTube video which describes the life cycle of ferns with very good animation!

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