Botany : specially written to meet the requirements of teachers' D, matriculation, public service entrance, intermediate and pharmacy A examinations

THE SEED AND GERMINATION. PRELIMINARY

Before dealing with the seed itself it will be necessary to learn how to test certain substances it contains, and to identify two gases, one needed for germination, the other produced thereby.

Oxygen may be prepared by heating in a test tube about a quarter of a teaspoonful of chlorate of potash mixed with a very small quantity of black oxide of manganese. After sufficient heating, a glowing splinter of wood plunged into the tube will burst into flame. Taking it for granted that the substance given off is oxygen, we have discovered the following facts. Oxygen is a colourless gas without taste or smell, and vigorously supports combusion. The fact that substances burn in ordinary air, though not so violently as in pure oxygen, would naturally lead us to suppose that the air is diluted oxygen. As a matter of fact, in five gallons of air we have about one gallon of oxygen, diluted with about four gallons of an inactive gas called nitrogen. Eight-ninths of the weight of water is also oxygen. Oxygen is a very active gas, combines readily with a great many substances, and in the act of combination, gives off heat. This combining of oxygen with some other substance is called oxidation, and the substance with which it combines is said to be oxidised. Under certain circumstances, the oxidation may be very violent and produce, at a given moment, much heat and light. In such cases we call it burning. When coal burns in a fire we have this fierce oxidation. The oxygen of the air combines with 27

the coal very rapidly and much heat and light are produced. On the other hand, when oxygen combines with iron to form rust, we have slow oxidation, and, though the total heat given off is considerable, it is produced so slowly that the iron never gets appreciably hotter. Nevertheless, if a coil of fine wire be heated red-hot at one end and held in a jar of oxygen, it will burn fiercely and produce much heat in a short time. The great function of oxygen in the living world is to oxidise things and set free heat and other forms of energy. Energy is the power to do work. All know the work that can be done by the burning or oxidation of coal. The heat given off may be used to warm a room, drive a locomotive, or to produce the electricity necessary for lighting or for driving a tram car. Neither animals nor plants could exist without oxygen. Animals absorb it through their lungs and use it to oxidise the food they have taken through the mouth, and thus to set free the energy they need for the body work. Plants, as we shall see later, use oxygen for the same purpose.

Carbon is a solid substance found in every tissue that goes to make up plant or animal. The diamond is pure carbon, while graphite, charcoal, coal, and coke are more or less impure forms of the same substance. The presence of carbon in any organic material may be indicated by heating it in a test tube, when the presence of carbon is shown by the charring of the substance. Thus milk, meat, wood, leaves, sugar, starch, and bone will all char when heated, for all contain carbon. In most plants, at least one-half the dry weight consists of carbon.

Carbon-dioxide is a gas which is usually prepared in the laboratory by pouring hydrochloric acid on marble chips. If these materials are not available the studend may, however, obtain the gas by pouring

vinegar on washing-soda in a test tube. Effervescence takes place owing to the bubbles of carbon-dioxide given off.

Carbon-dioxide is a very heavy gas, and can be readily poured from one vessel into another. Before pouring the vinegar on the soda have ready another test-tube containing about an inch of lime-water. Without allowing any of the liquid to pass over the lip, pour the gas from the first test tube into the second. On shaking the tube the lime-water becomes milky, and this milkiness is the recognised sign that carbon-dioxide is present. Now blow through a glass tube into clear lime-water, which, by becoming milky shows that the breath is heavily charged with carbondioxide. Next pour some lime-water into a shallow dish and expose it to the air. A milky scum soon forms on the top, showing that the air contains a certain amount of the same gas.

Now pour some lime-water into a jar of air, or better still, of oxygen. The liquid does not become milky, for in the small quantity of air enclosed in the jar there is not enough carbon-dioxide to produce an appreciable result. Now lower into the jar a burning candle, and withdraw it, when, having used up almost all the oxygen, it is about to go out. Then shake up the lime-water: it will become milky, showing that the carbon of the candle has combined with the oxygen to form carbon-dioxide. In the same way the carbondioxide of the breath is formed by the oxidation of the carbon in the food. It will be shown that a similar process of oxidation, producing carbon-dioxide, goes on in the plant.

Iodine in the dissolved state is used as a test for Starch, and may be prepared as follows:-

Dissolve a few crystals of potassium iodide in water, (about 1 gram to 75cc of water), and add to this iodine crystals till the liquid is a dark brown.

To show the test, make a little thin starch paste. A single drop of iodine added to this will give a blue colour. In testing substances for starch, the best results are obtained by scraping the material very fine, boiling in a test tube with water, cooling by letting the tap run on the tube, and then adding the drop of iodine, The cooling is very important, for, when the material is above a certain temperature, the blue colour will not appear. Various substances, such as potato, parsnip, and seeds may be tested in this way.

Fehling's Solution is a substance used to test for grape sugar, which is present in various parts of plants.

The following rough and ready method of preparing the Solution will serve all practical purposes:-

Add tartaric acid to bluestone (copper sulphate) dissolved in water, till the colour is slightly green, and then add caustic soda till the solution is dark blue.

To show the test, crush a piece of apple or banana, cover with water, add a drop of Fehling's Solution and boil in a test tube; a yellow or orange red sediment is formed, showing the presence of grape sugar. The carbon of the sugar has taken away from the copper in the solution some of the oxygen that was united with it, and thus caused the change in colour from blue to yellow. In other words the higher oxide of copper has been reduced by the carbon of the sugar to a lower oxide, which, being insoluble, has been thrown down as a precipatate.

Carbohydrates are solid substances that consists of carbon combined with the elements of water or, since water is a compound of oxygen and hydrogen, carbohydrates may be said to be formed from carbon, oxygen, and hydrogen, the oxygen and hydrogen being in the same proportion as they are found in water. The most important carbohydrates are sugar, starch, and cellulose.

Sugar differs from the other two in being soluble and in having more oxygen and hydrogen in its composition. Sugar, as we shall find later, is abundant in most fruits as well as in many roots and succulent stems. Starch is insoluble in water and is present in most seeds and underground stems. Cellulose forms the bulk of all wood, while good filter paper as well as cotton wool are pure cellulose. The simpler tests for this substance are not always reliable, but the following can usually be applied with success:-

Soak the material to be tested, say cotton wool or filter paper, in weak iodine solution and then place on it a drop of strong sulphuric acid. A blue colour appears, which almost immediately changes to black. Where this blue colour shows itself we may be sure that cellulose is present, but where it is not seen we cannot be so sure than it is absent.

Oils, which, like carbohydrates, are composed of carbon, oxygen, and hydrogen, but in different proportions, are plentiful in many seeds. In seeds such as the castor bean the presence of oil may be shown by rubbing the broken surface of the seed on a piece of tissue paper. A transparent greasy mark shows that oil is there. Where not plentiful, the oil may be extracted by crushing and soaking a number of seeds in ether in a tightly corked test-tube. The ether dissolves out the oil: after allowing the tube to stand for some hours, pour off the ether without disturbing the sediment of crushed seed, and allow it to evaporate in a shallow dish. When the ether has disappeared drops of oil will remain.

Proteins are found in all plants. Carbohydrates and oils contain carbon, oxygen, and hydrogen. The same three substances are found in proteins, but in addition, the gas nitrogen, the mineral sulphur, and, as a rule, the element phosphorus enter into their composition. Proteins then, are the nitrogenous