My Science School

Have you eaten an uncooked ripe tomato? Usually we consider the tomato a vegetable and use it in curries. However, it looks like a fruit in all respects. So, what is a tomato, a fruit or vegetable?

What makes a fruit different from vegetable? Vegetables do not contain seeds in them. Therefore, radish, carrot, celery and lettuce are vegetables; whereas, many vegetables, which we have never considered fruits even in the wildest of imagination, are, in fact, fruits! The tomato, therefore, is a fruit, no doubt. Along with it, beans, cucumber, squash and many more are fruits too.

However, we hardly eat them raw. Most of these ‘fruits’ are used as vegetables; and therefore, we call them vegetables out of habit.

 

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Fleshy fruits have many kinds of seeds. They are generally classified as berry, drupe, aggregate fruits and false fruit.

There are usually several seeds in a berry. Grapes, tomatoes and gooseberries are examples of berries. These fruits change their colour in order to signal when they are ready to be eaten. Drupes, on the other hand, have seeds inside them. These seeds are also known as stones. Mangoes, cherries, peaches and apricots are drupes. When animals eat these fruits, they drop the hand seeds on the ground eating only the flesh.

An aggregate fruit is not a single fruit. Many fruits join together to form an aggregate fruit. In fact, each individual fruit is formed in a separate ovay, and has its own seed and flesh. However, when they grow, they look like a single fruit. Raspberries and loganberries are aggregate fruits.

False fruits are counterparts of true fruits. While true fruits develop from a plant’s ripened ovary, false fruits develop from its ripened ovary together with other parts of the plant. The apple is an example. While the core of the fruit is from the ovary, the outer part of the fruit is grown out of the stem of the plant.

 

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Have you seen soft and furry parachute like dandelion seeds that fly in the air? In the wind, they fly to distant places, where they fall and germinate. Thousands of plants like dandelion produce seeds with a furry crown. They float away in the air, proliferate and propagate their species when they fall on the ground.

Many dry fruits explode when they are ripe. When they snap open, their seeds shoot to a distance. The pods of these fruits have two halves that split apart when they are dry. They explode with a loud noise. Cranesbill fruits are like tiny catapults. When they dry, tension builds up inside them and part of the fruit snaps, flinging seeds to the air.

If you have spent time on grassy lands, you must have come across certain itchy seeds with little spines or hooks. They get stuck to your clothes and are also easily lodged in the fur coat of animals. Thus, they move to distant places. Bur seeds are examples.

Plants that live near rivers and oceans have fruits that can float. Our coconut palm is a perfect example of such a plant. The fruit travels wherever the water takes it. It can survive in seawater for many days. When it finds dry land, it takes roots there, and starts growing. That is why seashore plants are found in various parts of the world.

 

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Seeds propagate a plant’s life. Therefore, plants package them in beautiful and secure cases called fruits. Nature, in its infinite wisdom, has devised plans to spread the life of plants in the most effective way.

Plants have developed ways to scatter their seeds. Some plants have exploding seedpods that fling seeds far and wide. For some other trees, the wind carries their seeds to distant places. Sometimes, water too comes to their help. Animals play a significant role in spreading seeds. Many plants have fruits that get lodged in the fur of the animal. The animal carries the seeds wherever it goes and deposits them somewhere safely.

Some seeds come in sweet and delicious berries. Animals and birds eat them. However, the seeds remain undigested in their belly and fall to the ground through their droppings. Have you seen banyan trees on top of some very tall buildings? Bird deposited the seeds there through their droppings.

 

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Yew trees are coniferous plants. However, they are a bit different when it comes to their cones. Yews do not have cones; instead, their seeds come in bright, red fleshy cups, known as an aril, which is open at the tip. They look more like berries than cones. But, beware! Most parts of a yew plant are poisonous!

The tree can grow up to twenty metres and live very long. The leaves of the tree are needle-shaped and dark green in colour. An evergreen tree, yews have male and female trees.

Yew trees have been associated with churchyards for a long time. Most graveyards in England have yew trees in them. It is a long held view that the trees were planted during the time of the plague in order to protect and purify the dead. The graveyards were inaccessible to cows, because eating the leaves of yew plants would kill them.

While the trees were symbols of death, they were also hailed as trees of immortality. For many centuries, it was a custom to carry the yew branches on Palm Sunday, and at funerals.

 

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Among coniferous plants, there are three major orders. They are cycads, ginkgoes and conifers. Cycads are one of the most primitive plants that bear seeds. They resemble ferns in many ways.

There are about 150 species of cycads. Some of them are found in very remote and restricted areas. Many cycads trees bear poisonous seeds, which look like nuts. The contie, a small and tough cycad, produces a starch called Florida Arrowroot or sago, which is edible.The plant is also known as Sago palm.

Some cycads have tuberous underground stems. Some have leathery, fern-like leaves and others have a columnar stems, which are often mistaken for palms.

 

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The welwitschia is probably the strangest plant in the world. While most known plants shed their leaves at some point in time, this plant never sheds its leaves. The plant consists of two leaves, a stem base and roots.

The uniqueness of the plant lies in the fact that the two leaves that the plant has will stay on it for as long as the plant lives. However, do not think that the plant has a short life span. It lives for centuries! The average lifespan of these plants is 400 to 1500 years. Many welwitschia plants alive today are 500 to 600 years old and some large ones are thought to be 2000 years old.

The two permanent leaves of the plant never cease to grow. They are broad and as hard as wood. They lie on the ground, and look like torn and shred ribbons in their appearance. There are male and female plants. They flower from summer to autumn.

 

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Large, tall trees are found in most places in the world. However, the American state of California is where the largest and tallest trees are found.

Conifers, as we have already seen, make the largest and the tallest trees in the world. Such trees are found abundantly in California.The largest conifers are the giant sequoias of the western United States. The biggest among this species, the General Sherman tree, is located in the Sequoia National Park, in California.

The redwoods are the tallest trees in the world. The tallest redwood is 115.7 metres high, and is in California. These trees are slimmer than sequoias, yet more graceful than them. Therefore, as far as trees are concerned, California is the home of the tallest and the largest.

 

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As we have already seen, not all plants reproduce through flowers. Coniferous plants have cones that carry their seeds. They are also known as gymnosperms. The word ‘gymnosperm’ comes from two Latin words, ‘Gymno’, meaning ‘naked’, and ‘sperma’, meaning ‘seeds’. Coniferous plants have exposed seeds in their cones.   Cedars, cypresses, fires, junipers, kauris, larches, pines, redwoods, spruces and yews are examples.

There are more than 600 diffrent species of coniferous plants. In most plant species, both male and female cones occur in the same plant. Male cones are smaller than female cones. They produce pollen during the springtime. These plants depend primarily on the wind for pollination. Coniferous plants are found across the globe.

Coniferous plants can grow into huge trees. Some of world’s tallest, widest and oldest trees are conifers. The leaves of coniferous plants are of three types. They are needle-shaped leaves, flat leaves and scale-like leaves.

 

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Have you smelt the leaves of a tulsi plant? It smells sweet. So do many other flowering plants such as roses and jasmines. While some flowers have a very attractive fragrance, some others do not have any smell at all. Some other plants have a repulsive smell too.

Flowers and plants have strong smells in order to attract pollinators. Insects are attracted by their smell. These flowers usually have a sweet fragrance; however, there are flowers that have strong stink too. Little flies come to these flowers that give out the smell of rooting meat.

Not all flowers have a fragrance. Plants that pollinate through the wind do not need colours or smell. The flowers that grow on grasses do not have any smell because they rely primarily on the wind for their pollination. Flowers in light colours such as yellow, pink and white attract moths and butterflies that can see. These flowers usually have a faint smell and not a strong one. Flowers that bees frequent do not have any smell generally. Bees see their colours and are attracted to the flowers.

 

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Sleep is essential for all animals. It gives necessary rest to our body and mind. In a way, plants sleep too; but not in the way we do.

Plants sleep when it is dark and there is no Sun. Since, in the absence of the Sun, they cannot make food, and photosynthesis is not possible. Therefore, during night, plants close down their stomata and only respiration remains in them, much like animals. Some plant species even fold their leaves in the dark.

Organisms have adapted to the rhythm of night and day. Scientists have been studying the day and night rhythm in plants. They say that plants sleep during the night. Flowers open in the morning and leaves close in the night. Carl Linnaeus observed that plants continued this behaviour even when they were confined inside a room away from the Sun.

Some big trees reportedly droop downwards in sleep during night. When dawn approaches, they come back to their old self, the same way we get up in the morning.

 

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We sweat after a hard day’s labour. Sweating is a way to control the heat of our body. What do plants do when they have excessive heat? Scientists say that plants sweat too, although not the way we do.

Plants release water from their leaves incessantly. However, this may not be visible to us. If you cover a plant with a plastic bag, you will see droplets of water formed on the leaves. These droplets are, in fact, the sweat of the plant. Sometimes, people mistake the water found on the leaves of plants in the morning as dew drops. In fact, the plant was sweating during the night. The process of a plant’s sweating is known as transpiration.

During transpiration, plants expel water through the tiny pores on their leaves called stomata. These pores can close and open in order to control the loss of water in a plant. Sometimes, the amount of water that a plant releases can be very high. It is said that, over a growing season, corn growing in one acre of land may transpire 15100 litres of water!

 

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You may have heard about walking trees in fairy tales. Trees do not have the ability to move about from place to place like animals. However, trees do make certain movements.

Plants move when they grow. Their movement is so subtle that we are hardly able to notice it. A growth substance called auxin is found in plant cells. This substance helps plants move in the direction of the sun. Due to the presence of the substance, when we plant a seed, its sprout will grow upwards towards the sky. Botanists call this phenomenon geotropism.

Plants move in various ways. Some vegetables such as pumpkin and bitter gourd can reach up to objects with their tendrils. Flowers move as they open and close their petals. You may have seen sensitive mimosa plants that wilt when someone touches them.

Fruits of porcupine grass can move their long tail. There are plants such as the witch hazel that shoots its seeds when they are ripe. A jumping bean moves when the caterpillar inside it jumps.

 

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Plants are stationary beings that stay in one place for ages. Some consider them witnesses of the events that happened in a certain place. Sometimes, divinity is even attributed to them, and people worship them. Can trees see as we do?

Some plants such as the sunflower respond to the presence of sunlight and move in that direction. The sensitive, touch-me-not plant quickly folds its leaves when someone touches it. All these facts give us the impression that plants do have the faculty of touch. However, since they lack brains, we cannot conclusively say that they can see, hear or feel pain.

Plants, however, have the ability to respond to external stimuli as is evident from the examples of the sunflower and mimosa plants. Scientists, on the other hand, think that trees lack faculties such as hearing, smell, seeing and feeling the way we have them.

 

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Trees have different life cycles. Some trees live for a short time, while some others live for centuries. Plants are named annuals, biennials and perennials depending on the length of their life cycles.

Annuals live for a year. They grow, produce flowers and die within the span of a year. Plants such as petunias and zinnias are annuals. When these plants die, they leave seeds that will grow into new plants. Not all such plants live for an entire year. A seed-to-seed cycle can occur in the span of even a month. Many desert plants live for only a week and thus they are called ephemeral.

Biennials live for two years. In the first year, the tree spends time storing its food for the winter months. The tree produces flowers and seeds in the second year and the tree dies later. Turnips, carrots and beets are biennials.

Perennials live for more than two years. Such plants do not flower in the initial years. However, in course of time, they flower and fructify and repeat it every year. These plants grow into huge trees and occupy more space than other smaller plants. Most perennials can be grown from cuttings or seeds. Chrysanthemums, peonies, irises and lupins are some popular perennials found in gardens.

 

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