My Science School

            An affirmative reply to this question is amazing but true. It is a fact that many trees can produce the fruit of another kind of tree by a simple method called ‘grafting’. It is an artificial method or technique of vegetative reproduction in which a small branch or bud of any desired plant is inserted into another rooted plant. This is called plant propagation. If a bud from a twig of pear tree is carefully inserted in a slit made in the bark of a quince bush, a pear twig will grow. The quince bush will bear both pears and quinces.

            In the same way, an almond tree can be made to produce both peaches and almonds. Although sometimes grafting is used to produce freak trees and bushes, this technique is of immense importance in agriculture. Lots of experiments in this field are still being carried on to produce better and new varieties of fruits, flowers and corns etc.

            The greatest advantage of grafting is that it can be used to better the quality and quantity of a particular product. It is possible for a nurseryman or gardener to be sure that his young trees or shrubs will bear the same quality and variety of fruit as the parent tree. A twig taken from a tree and grafted into another tree will produce the same type of fruit borne by the tree from which it was taken.

            There are many methods for inserting the budded twigs or scions, as they are called, into the stock of another plant, but two rules must always be followed. First, only related species of trees or shrubs can he grafted. This implies that apples can be grafted onto pear and quince trees, and peaches can be grafted onto apricot, almond, plum or other stone fruit trees. It is impossible to graft apples on a peach tree. Secondly, the cambium layer (a layer of actively dividing cells) which carries the vital sap of scion must touch the cambium layer of the stock on which it is grafted. Otherwise the grafted twig cannot grow.

            There are different techniques of grafting. It can range from inserting a single bud under the bark to grafting long twigs across the wound of a tree in order to heal wide wounds in the bark. Tissue culture is popular these days in which cells from a plant are removed to propagate in another plant to obtain a hybrid product or the product of the original plant.

            The technique of grafting is now widely applied in case of animals as well as human beings. There have been surgical operations in which a bone taken from the ribs has actually been grafted onto the nasal bone to form a new nose. But the best application is in cases of severe burning where the healthy skin from one part of the body is grafted onto the burnt tissues to remove scars.

               One of the fundamental differences between plants and animals is that animals can move from place to place whereas plants lack mobility. But inconsistent with this general distinction, there are some plants which move on their own. For example, slime molds have amoeba like movement whereby they ‘coze’ from one place to another. Some types of algae have whip like flagellas, they use to paddle themselves through water. Many plants particularly, the lower ones, produce mobile male gametes which swim about in order to find eggs to fertilize. Englena is a protozoa which is capable of swimming. Apart from these exceptions, the movement of plants is usually confined to the movement of some parts of it while the plant itself remains fixed at one place.

               There are three basic types of plant movements: tropisms, nutations and nastic movements. 

               A tropism is a growth response towards or away from something caused by a specific environmental stimulus. The direction of growth is determined by the stimulus. When it is towards the stimulus, it is caller positive tropism and when away from it, it is called negative tropism.

               Tropisms are caused by special growth hormones called auxins. In most of the cases, the stimulus causes the auxins to collect on one side of an affected organ. This causes the cells on that side to grow and divides more quickly than the cells on the other side. As a result, the organ bends away from the side with the most auxins.

               Tropism is of several types. Phototropism is a growth response to the stimulus of light and auxins are concentrated on the side away from the light. This causes stems and leaves to grow towards light and roots grow away from light. Geotropism is the growth towards the gravity of earth. Roofs show positive geotropism while stems show negative geotropism. Hydrotropism is the growth response to the stimulus of water. Roots grow towards water and often move great distances to areas of moist soil. 

Continue reading "Do some plants also move? "

          The oil that we use in our kitchen or for the manufacture of margarine and other goods is obtained from the seeds of many plants. The world production of major oilseed crops (in millions of metric tons) is Soyabeans 46.5, Peanuts 18.1, Cottonseed 22.1 and Copra 3.4. The other sources of vegetable oils are mustard, rapeseed, sunflower etc.

          The basic process for extracting oil is essentially the same for all oilseeds. It involves either pressing or solvent extraction or a combination of both. The material that remains after removal of the oil contains primarily fibres, carbohydrates and proteins. This may contain protein upto 50%. This material is discarded and used as fertilizer or animal feed.

          Most of the world’s supply of coconut oil comes from West Africa. It is taken from the dried kernel of the nut called copra which contains 70% oil. Palm oil also comes from West Africa and from South-East Asia. These oils are produced in a hard fatty form called stearine, which is used in the manufacture of chocolate, cooking fats and medicines. Crude oil is used in soaps and shampoos.

         Cottonseed provides about 37% oil. The cotton plant is grown commercially in the United States, India and Egypt. The fruit of the plant splits open to reveal fluffy white fibres and a number of seeds – each about six millimeters long. Cottonseed oil is used in margarine, cooking fat, and salad oil. It is also used in soaps, resins, grease and lubricants.

         Linseed is the seed of the flax plant which is grown primarily in the United States, Russia, Argentina, India and Canada. Flax fibres are woven into linen cloth and the seeds are used for extracting oil. Linseed oil is used in paints, varnishes, printing and lithographic inks, linoleum, oil cloth and as a water-proofing agent. The residue is a valuable cattle food.

         Groundnut or peanut is the seed of the plant Arachis Lypogea. The seeds of this plant yield oil and are cultivated mainly in China, West Africa, the United States and South-East Asia. It is mainly used as a cooking medium.

         Soyabean is the most important of all the oil seeds. It is extensively grown in China and the Far East. Soyabean oil is used for cooking and as a base for paints, plastics, adhesives, etc. It is a rich source of protein. The seeds can be ground into protein-rich flour which can be used in many foods.

          Sunflower is becoming increasingly popular in European oil markets, and so is rapeseed in Canada and Northern-Europe. Sunflower is now grown in countries like Mexico, Russia, erstwhile Yugoslavia, Turkey and South Africa.

 

            Anything exposed to the sunlight for some time becomes very hot, especially during the summer months. A scrap of paper or a piece of metal kept in the sunlight may even become too hot to touch after a while. But have you ever wondered why the leaves of trees and plants, which are exposed to the sun the whole day, don't get so hot?

            This fact may be understood as follows: a plant leaf is made up of several layers of cells. The upper epidermis covers the top surface of the leaf and the lower epidermis covers the underside. The lower epidermis has many openings called stomata, which act as valves. They regulate the exchange of gases between the leaf and air. When they are open, they allow carbon dioxide to go into the leaf. They also release oxygen and water vapour. When the stomata are closed, inhaling or exhaling cannot take place.

            Each stomata is surrounded by two sausage-shaped guard cells, which control the size of openings. The stomata are usually open during the day and closed at night. The water vapour that is lost by the leaf through the stomata is replaced by water from the roots. This process is called transpiration.

            So when water evaporates, it cools the leaf. Hence this enables the plant to keep cool in the sunlight.   

The roots of certain plants get swollen with stored food. They can be eaten as vegetables. The plants that produce such roots are called root crops.

Root crops have long been cultivated as a food source all over the world. Since they extract different chemicals from the soil, as against grain crops, they have proved useful in crop-rotation systems.

The roots of beet are consumed mainly in cooked form and are usually served with a main course or in soups. Beet powder is used as a red colouring agent in sauces.

Carrots are bright orange-coloured roots. They contain high percentage of carotene. They are consumed in fresh or cooked form and are sometimes dehydrated.

 

Continue reading "Which are the roots we eat? "

          Do you know that there are certain plants which cannot produce their own food because of the absence of chlorophyll? Such plants, therefore, depend on other plants or dead animals for their food.

          Plants which feed on dead organic matter are called ‘saprophytes’ and those which feed on plants are called ‘parasites’. Saprophytes play an important role in the decay process. They clear the land of dead animals by digesting and absorbing nutrients from the dead material. For instance, all fungi and bacteria which do not contain chlorophyll fall in this group.

          Parasitic plants feed on other plants. They obtain water and food from the host through specially developed organs called ‘haustoria’ which secure the parasite to the host and grow into the host’s tissue. Parasitic plants do not give any benefit to their hosts in anyway. In some cases, they cause harm to their hosts.           

          The extent to which a parasite is dependent on its host largely determines its vegetative form. True parasites such as dodders, cuscuta and cassytha are entirely devoid of chlorophyll and rely entirely on the host as a food source. The dodder, which is a well-known parasitic plant, looks like a tiny slender snake. Its colour varies from bright yellow to red. When a dodder seed germinates, the young plant begins to grow in a circular fashion, searching for the mother plant. Once it gets a host, the thin stem of this plant twines around the host’s stem and starts taking food from the host.

          Other parasites such as the toothwort and the broom are parasitic on the roots of other plants, rather than their stems. Correspondingly, these plants are less conspicuous than dodders because their vegetative parts are underground.

          A well-known example of a partial parasite is mistletoe which grows as a cluster of branches hanging from trees. It produces a haustorium which connects with the host’s stem and extracts water and mineral nutrients. It can produce food by photosynthesis but needs water and minerals from trees.

          Mosses and lichen are also parasitic in nature. They cover the bark of the trees and take food from them. Rafflesia Arnoldi of Sumatra is also a famous parasitic plant.

 

          Banana is a popular fruit and an important part of our diet today. It originally belongs to South-East Asia and the Indonesian region where it used to grow wild in the forests. Over the years, proper selection and cultivation of different varieties yielded the ‘edible’ banana. By the beginning of the Christian era it had already become a popular fruit in the Asian and Mediterranean countries. When the Spaniards settled in South America, they planted it there and being a tropical plant, it grew well. 

          The banana tree grows round the year in hot and moist climate. Bananas are picked when they are still green and left to ripen while being transported.

          Banana is a wholesome food. It is made up of water (75%), sugar (20%), proteins (2%), fats (1.5%), cellulose (1%), and other substances (1%). It also contains vitamins such as A, C, B1 and B2. It is quite a nourishing and easily digestible fruit. Half a kilo bananas contains 460 Calories and are more nourishing than any other fruit. A type of flour is also made of dried banana. In American and Asian kitchens bananas are used uncooked in salads and with ice creams. In Africa people thatch roofs of their huts with the banana leaves. 

          The plant yields a kind of fibre which is used to make ropes.

          There are over 200 varieties of banana belonging to about 30 species. They are never grown from the seed but are produced by planting of rhizome pieces. The new plants grow up amazingly fast from the buds. Its height varies between 5 to 30 ft. Each plant has about 10 large leaves and bears a single bunch of fruit. The banana leaves are about 6 to 7 ft. long and 1 to 2 ft. wide.

          Today, the United States is the greatest buyer of bananas, consuming more than 60 million bunches every year. 

          Man has been using garlic since ancient times to add flavour to food. Garlic has a powerful smell and a pungent taste. The Roman soldiers believed that it helped them in being more courageous and stronger so they made it a point to include it in their regular diet. In the Middle Ages garlic was eaten as a defence against the plague. It was also worn on the body to ward off evil spirits.

          It is only a few years ago that man discovered its medicinal importance. Its bulb contains an antibiotic called allium.

          It has antiseptic properties and is used for curing intestinal disorders. It is highly effective in controlling high blood pressure. It is also being used as an effective remedy for heart ailments and cough.

          Some people crush it and rub it on the skin as a cure against insect bites and stings. Some people make syrup out of it and drink it to cure cold. Gardeners put garlic in the soil around peach trees, to discourage borer from entering and damaging the trees.

          Garlic plant is native to Europe and Asia but it also grows wild in Italy and Southern France. Garlic produces two types of bulbs or bulbets. The aerial bulbets produced on the flower stalk are used as seeds to new plants. It is grown as an annual crop. The underground bulbs, called cloves, are the one sold in shops. They are formed at the base of the plant much like an onion. One bulb encloses up to 20 bulbets. Garlic contains about 0.1% essential oil, the principal components of which are diallyl disulfide, diallyl trisul-fide and allyl propyl disulfide.

          All living beings breathe in order to survive. In the process of breathing they inhale oxygen and exhale carbon dioxide. Oxygen combines with hydrocarbons to produce energy and carbon dioxide.

          Plants are living beings and they also breathe to survive. The only difference between animals and plants, in this regard, is that while the animals inhale oxygen and exhale carbon dioxide, the plants inhale carbon dioxide and exhale oxygen during the day and inhale oxygen and exhale carbon dioxide at night.

          The leaves of plants take in carbon dioxide from the air during the day. A green substance called chlorophyll, that is present in the leaves, converts it into sugar and water. This process is known as ‘photosynthesis’ and it takes place only in the presence of sunlight. The oxygen produced in this process is discharged into the atmosphere and sugar is used up as food by the plants. This sugar gets converted into carbohydrates, carbonic acid and vitamins.

          During the night, when there is no sunlight, the process of photosynthesis comes to an end, during this period plants make use of some part of the sugar produced in the daytime. They take in oxygen from the atmosphere and give out carbon dioxide that is why it is not advisable to sleep under a tree in the night.

 

          The new leaves of any plant appear pink but after some time they turn green. Do you know what the reason behind it is?

          We know that the colour of any substance depends upon its property of absorption and reflection of the different colours of light. The leaves of the plant appear coloured due to the presence of some specific substances in them. For example, the presence of chlorophyll makes them appear green while the presence of carotenes makes them yellow.

          When many substances are present in one leaf, it shows the colour of the mixture. The leaves which contain both chlorophyll and carotene appear yellowish green.

          New leaves of some plants contain a red substance called anthocyanin, which gives the pink or red colour to the tender leaves. With the passage of time, chlorophyll and carotene are formed in these leaves, which ultimately turn them green.

          The structure of chlorophyll molecules is such that when the sunlight (mixture of seven colours) falls on them, they reflect the green colour and absorb the rest. This reflected green colour reaches our eyes and gives the green appearance to the leaves.

          Plants synthesize their food with the help of chlorophyll in the presence of the sunlight. This process is called ‘photosynthesis’. Plants without chlorophyll like fungi cannot make their own food. They depend on other living beings. Such plants are called parasites.

          In this way, we see that chlorophyll is a very important substance for plants which gives them the green colour. 

          Most of the trees and plants shed their leaves during autumn and new leaves sprout on them during spring. After the defoliation they appear quite barren. The trees which shed leaves every year are called ‘deciduous trees’. However, there are other trees which do not shed all their leaves at one time, and thus always appear green. Such trees are called evergreen trees. Do you know why this happens so?

          In fact, all the trees shed leaves. But the leaves of the trees which undergo defoliation every year live only for one year. On the other hand leaves of the evergreen trees last for two to three years. As soon as a leaf withers it falls down and a new leaf sprouts in its place. Thus all leaves are not shed at a time. As a result the tree always retains a large number of leaves and this cycle continues. 

          Among the well-known evergreen trees are pines and firs. Besides these, there are many other trees which always remain green. The Italian cypress found in Europe is one such tree. The olive plant also comes under the category of evergreen plants. Its oil is very useful for us. The magnolia plants are used for decoration because their white flowers are very beautiful and do not have defoliation. Perfumes are extracted from the evergreen plants of the rosemary. The juniper plants, having short and bitter leaves which are found in North Britain, are famous for their greenness. In addition to these, other evergreen plants and trees are myrtle of Britain, oleander of North Africa, oak tree, ivy creeper, orange tree and tall palm tree. The tea plant also comes under the category of the evergreen plants.

 

          Whenever we pass through a garden during the spring the fragrance of flowers enchants us. Nature has endowed flowers with beauty, attractive colours, nectar and fragrance. Insects and flies get attracted towards the flowers and sit on them. And when they leave they carry with them pollen grains to other flowers. This dispersing of pollen grains helps in the pollination of flowers, as a result of which, seeds are produced. In this way plants and trees multiply on their own.

          Different flowers contain different oils which give specific fragrance to flowers. As these oils gradually keep on evaporating, the fragrance of the flowers spreads in the air. In fact, perfumes are prepared from the oils extracted from these flowers. There are various processes of making perfumes. In one process, flowers are kept in a pot through which steam is passed. The outgoing steam brings oil with it. This steam is passed through water. Thus the oil brought out by the steam starts floating on the water surface. This is then separated from water. There are other methods of making perfumes also. France produces the maximum amount of perfumes. It has been found that one ounce of rose perfume is extracted from 110 kgs of rose flowers.

           Flowers like rose, Raat Ki Rani, Pandarus, lavender, jasmine etc., are generally used for making perfumes.

           The anthocyanin pigment is responsible for producing red, blue and violet colours. The plastid pigment causes other colours. These pigments remain mixed in the juice of the flowers. The presence of chlorophyll and carotene make some flowers green. There are at least 200,000 kinds of flowers, ranging in size from the microscopic duckweed blossom with a diameter of 0.4 mm to the tropical Rafflesia with a diameter of 90 cm. 

          On the basis of age, plants are divided into three categories: annuals, bi-annuals and perennials. The annuals are those plants which take birth, grow up, give fruits and die within a year. Wheat, barley, gram, peas, tomato - all live for one year only. The bi-annual plants live for two years. In the first year they bear only leaves, and in the second year - flowers and fruits, and after that they die. Plants like the ‘fox-glove’ and the ‘hollyhock’ come under this category. The perennial plants live for more than two years. Generally they are called trees or bushes. They blossom and bear fruits many times. The trees of the neem, mango, jamun (black plum), guava etc. come under this category. Some perennial trees have a life of more than 4000 years. The great sequoia trees found in California are reported to have a life of more than 4000 years. The yew trees live for 3000 years. The chestnut and the oak trees live for 2000 and 1500 years respectively.

          Now the question arises: how is the age of any perennial tree determined? Scientists have devised a very simple technique to do this. This technique refers to the number of rings present in the trunk of a tree. If you cut off a slice from the tree trunk, you will notice many concentric rings in it. These rings are the record of the tree’s age. In fact, the trunk, underneath the bark, keeps on growing thicker with age. However, the wood which grows in winter and autumn is denser and harder as compared to that grown in spring and summer. This results in the formation of a ring in the trunk every year. These rings are of brown and cream colours alternatively. Thus the number of rings counted from the centre of the trunk of a tree tells its age in years. Its central portion is called the ‘path’.

          Some fruits like watermelon, guavas, grapes, apples, mangoes etc. are sweet in taste while lemon, orange, raw mango, etc. are sour. Each fruit has a distinct taste which differs in some way from the taste of any other fruit. The question arises: why does every fruit have a characteristic taste?

         In fact, the taste of any fruit depends on the compounds present in it. In general a fruit contains fructose (natural sugar), organic acids, vitamins, starch, proteins, minerals and cellulose. All these materials are in a mixed state inside the fruit and are found in different proportions in different fruits. Fruits having more fructose content taste sweeter, while those having more acids taste sour. Orange is a fruit which has almost equal quantities of fructose and acids hence it tastes both sweet and sour.

          In general, raw fruits contain more acids but on ripening, the quantity of acid in them decreases and the amount of sugar increases. Hence raw mangoes are sour, but ripe ones are sweet. Raw bananas contain more of starch, but it gets converted into fructose when the fruit ripens.

          During the process of ripening, chemical changes take place inside the fruit by which the quantity of sugar increases thus adding to the sweetness of the fruit.

          You will notice a difference of taste even in two fruits of the same kind. Two apples or two mangoes do not always taste alike. This is so because there are many varieties of the same fruit and also the variations in the quality of soil, climate, growing technique, manure, water etc. change the proportion of the compounds inside the fruit resulting in the difference of taste.

          Sour fruits like lemons; do not taste sweet even after they are ripe, because of the presence of excessive amounts of acids.

          Generally the edible-fleshy part with seeds which develops from the flowers of any plant is called a fruit, whereas trunks, leaves and flowers of herbaceous plants used as food are called vegetables. But scientifically speaking, the above definitions are not correct.

           According to botanists the part of the plant that carries seeds and produced by the ovary of a flower plant is called fruit and the remaining part used for food is called vegetable. Scientists have divided fruits into three categories (i) fruits with pulp and seeds such as apple, orange, watermelon etc. (ii) fruits with stones, such as plum, cherry, peach, etc., (iii) dry fruits such as almonds, walnuts etc.

          According to botanists, beans and peas also fall under the category of fruits. Cucumbers and marrows are also fruits. But cabbage, turnip, radish, cauliflower - all are vegetables. Onions, potatoes etc., are also vegetables.

          In USA a controversy over tomato went on for a long time. Finally the U.S. Supreme Court had to decide the issue. According to botanical sciences, tomato is a fruit but generally it is used as a vegetable. Keeping both the views in mind, the Supreme Court ruled in 1893 that tomato is a vegetable from commercial point of view. In science, however, this can be treated as a fruit. In reality, the scientific definitions of fruits and vegetables do not agree with the general usage. In our common language we treat some fruits as vegetables such as brinjal, peas etc. and some vegetables as fruits, such as raw banana.