PRACTICAL IRRIGATION.

Dominion, Volume 5, Issue 1336, 13 January 1912, Page 14

PRACTICAL IRRIGATION.

• PLANT LIFE.

(By John irKenjue.)

I. (Copyright.) In order to understand tho effects of irrigation in tho soil and on tho life and gTowth of plants, it is necessary first to understand how plants germinate, live, grow, a lid reproduco themselves;' and, further, what fresh conditions and effects are produced in tho soil by tho presenco of irrigating water. Some plants, as tho mistletoe, live and grow in air only; others, as the hyacinth, in water only, tint tho soil is tho birthplace, and the home of nearly all plants; and l'rom tho soil and the air all plant life derives its daily food. 801110 plants aro reproduced from cuttings; but most new plant life is ' derived from seeds. Plants and seeds aro separated into various classes, but for our purpose, which is to understand tho origin, the machinery, and tho conditions nocessary for the growth, the development, and the reproduction of plants, it is necessary only to understand the facts in relation to two common seeds—tho pea, and the seed of wheat. The Pea and Seed Wheat. Take a pea, and carefully examine it. Around tlio outside ij a skin of dead matter. Kemoye tho tiki 11, and the rcniainiug part will bo found to consist of two thick masses placed lace to face; and, further, these two thick masses aro united by a long-shaped body, which is joined to each mass. This long-shaped body is the embryo; and tho thick masses furnish iood for the germinated and growing young plant. Examine now the seed of wheat. The embryo hero consists of 0110 thick mass, which is placed at one side; the other sido consists of a white iioury substance. _ Take either of tlieso seeds, and place it in dry mould. So long as the mould remains dry, the seed will not germinate. Moisten tho mould, but keep tho seed and tho mould at or below the freezing point, and the seed will not germinate. Now placo tho seed ill moist mould, and in a temperature above the freezing point, but exclude tho air, and still the seed will not germinate, liut, if the air bo allowed to como in contact with tho seed, and to circulate through the moist, wann mould, the seed will germinate. Large quantities of oxygen, which is ono of th? gases of tho air, aro consumod by germinating seeds, and seed will not germinate in the absence of oxygen, hence the air must find its way freely to the germinating seed. Tho combination of oxygen with other elements is termed oxidation. It thus appears that three conditions aro necessary for the, germination of_ seed: (a) moisture, (b) ' warmth, (c) air. When the seed commences to grow, ono end of the longshaped body grows 'upwards, and forms the stem, and afterwards the branches, leaves, buds, and flowers of the new plant. The other end grows downwards, and. forms the root. In many cases this root descends to a great depth in the soil, and is known as .the tap-root, as in tho case of the pea and other plants of the same family. Rootlets generally grow and spread in all directions from the tap-root. In the case of wheat and other, surface-growing pjants, there- is not a tap-root. Rootlets, instead, grow and spread through the soil which surrounds the seed. The soft points of growing roots do not bore through solid clods or hrmly-packed earth. They push through the open spaces between tho particles of the soil; grow rapidly; and the hairs on the rootlets cling to the particles of uie soil, 111 which the plant, as a whole, is nnnly fixed. These hairs perform an important function in the nourishment of the plant. .Vvhen .the embryo has germinated, and commences to grow, the young plant at first receives nourishment trom tho thick masses to which the embryo was, and still is, attached. When the root is firmly fixed in tap soil, the plant, food is ho longer supplied by tho seed, but is taken directly from tho soil through tho roots; and from the air through the leaves. As soon as this occurs! two fresh conditions, in addition to those necessary for the germination of the,seed, are ifeodcd for tire growth and development of tho plant, namely certain portions of llic soil and light. The principal parts of most plants are: (a) The root; (b) the stem, or trunk; (c) the leaves; (d) the flower; and (e) tho fruit, which usually contains the seed. Each of theso parts 13 railed an organ, and oach organ has special work to do. Functions of the Organs. The function of the root is, to hold tho plant firmly in tho soil; to take up nourishment for the plant from the soil, and sometimes to' store up foodstuffs for the uso of the plant., as in the case's of the pea, wheat, turnip, mangel, and tho fruits. The function of the stem or trunk is to support the branches, leaves, buds, and flowers; and to act as a channel through which to convey the ■ nourishment from the roots to the branches, the leaves, the flowers, and the fruit. The function of the leaves is to nrovido a lare-e surface for exrwsing the plantfood to tho action of the sunlight and , heat, and to absorb the c.nrbonic acid gas : from the air. The functions of the flower ] md the seed are to bring about the reproduction of the plant.- i • The snbstance of which plants, and'the vegetable world, in general, arc formed is called tissue. This tissue consists of nunule colls. Each cell is a very small round body, Ami consists of <i Tiarent oufcsifle skin, which' encloses. in the living plant, the plant-food; When 1 0 m TS Nvo inside covins n»r only. Tllp plant-food in the livinsr cell consists of on active, living substance, called nrotonlasm. As the plant grows tho colls enlarge, the pathprs mto a small rnimil body in the centre of the cell. Fibres spre s nd out from * nnd ,'? itn C h themselves to th« sides 1 cell. In time, the cell : divides nml each portion forms a new cell. By this process of enlargement and division ot the cells, the plant grows and increases until it arrives at maturity. The leave* are continuous with the skin or bark of the plant or tree, and their formation is simple. Lay .a preen loaf on a flat surface nnd cut ft in two with o sham knife. Isow, examine the through a It will be seen that a thin and delicate skin covers the lenf on each side. .and immediately below the skin is a layer of closely packed cells. Towards the interior of the leaf several layers of loosely-packed cells are seen. The skin of the leaf has many minute openings. which open more widely in sunlight than in darkness. * The tissue of the plant proper is thus in complete union with tho tissue of the leaf, and tho circulation is complete and continuous from the roots to the leaves. The stem and the branches of a plant or txee are usually divided at' fairly rcrular. distances into sections. When the?e : join a. raised ring runs around tho stem or the branch. These raised riiiTs are called nodes, and it 'is from these rings that tho leaves ari?c. During antunm buds aro fonted, either at the ends of tho stems and branches or at the nodes. Tho bud itself and its circulation are also oontiuuous with the tissue of the stem. They are often protected from the cold by a covering of scales of resin, of gum, or of hairs. During winter, they remain as they were formed in nntuimi. Growth begins in the spring, and the buds develop into leafy branches, which mav form either leaves 'or flowers, or both. Instead of only growing longer, fliev may [stow in width. When the bud grows into a flower the" object is to' bring about the reproduction of tho plant by producing seed. The Perfect Flower. A perfect flower consists of (a) tho calyx; (b) the corolla; (c) the stamens; (d) tlie pistil.' From tho point where tho flower joins the stalk, separate pieces, generally of a green colour, form a row around the outside of the flower. This outside row is the calyx. Within tho calyx is a second ring of separate pieces. These are nearly always white or coloured, hardly ever green. This row is callod the corolla. It secretes a sugary juico or nectar, which attracts insects to tho flower. Within the corolla or seoond row is ia third row, usually formod of slender stalks, or stamens, and on the top of each stalk is a small vessel, which holds the powder, known as pollen, and which is necessary for fertilising the seed. Tho fourth ring assumes mora forms than any other part of the flower. | Its simplest form is the flower of the pea. The pistil of the common pea is simply a leaf folded down tho middle, with "its edges united to form a hol.low vessel, which contains the seed. If a flower has all these rows, it is a perfcct

flower. It any row bo absent, the flower is imperfect. The uso of the hollowvessel first mentioned is twofold. It secretes littlo grains wifliin its cavity. It also provides the means for conducting tho pollen from tho stamens to the interior. Tho pollen may be conducted either by direct contact of stamen with pistil, by" insects, or by tho action of tho wind. When the pollen has reached tho cavity, the little grains in that cavity are fertilised, and becomo seed, fitted, in due course, to reproduce the plant. Concerning Plant Foods. The food of the plant is derived from two sources—from the soil through its roots, and from the air through its leaves. The hairs of tho rootlets, as we have seen, cling to particles of the soil. The soil is a laboratory in which solutions of plant l'ood are compounded. The plant, ami especially the roots, exude acid salts, which have tho power, aided by water and carbonic acid, to dissolve aild bring into the plant various useful matters that wero previously lying outside the roots insoluble in water. Tho hairs of tho rootlets are formed of cells, or exceptionally ininuto bags. Tho outer skin of tho coll or bag is called tho walls of the coll. Those parts of the liqtiid solution thus formed in the soil, which are suitablo for the food of the plant, pass through the walls of tho cell, and by tho sauio process—much the same as that by which oil ascends a wick. The leaves absorb air through the same openings or pores. Inside the leaf tho air is resolved into nitrogen aud oxygen. Tho oxygen is liberated and the nitrogen incorporated with the plant food, which has arrived from the roots. The whole is exposed to the action of sunlight, and converted into plant food, much after the manner a housewife makes bread from flour, milk, salt, and yeast Tho housewife is Nature acting in tho shape of sunlight; tho flour, the salt, aud the yeast are provided by the conjuint action of the plant as the carrier from mill or laboratory in the soil; and the manufactured plant food is sent to every living part of tho plant to bo used for the growth, the sustenance, and tho reproduction of tho plant, in much the same way as a hungry schoolboy eats up his dinner. As the schoolboy wants water or tea with his food, so the plant requires water. The water ascends through the roots, branches, stem, and arrives at the loaves, not by passing from cell to cell, as tho plant food does, but chiefly through the fibrous parts of tho plant; and • it goes through these parts more rapidly than it could go from cell to cell; and the transmission of both plant food and water is much more rapid in sunlight than in darkness. There are thus two movements constantly going on in the living, healthy plant: (a) Tho movement of tho plant food from cell to cell; (b) tho movement of water from the roots to the leaves. The normal movements of tho plant food are both upwards and downwards from or to the factory or laboratory in the leaves. The Water Required. All growing plants and trees require a very large amount of water. Turnips contain over 00 per cent, of water, and water-cress 9G per cent. Tho water, having passed through the plant or tree, is exhaled by the leaves. If a window sash or other framed glass bo laid on grass, tho glass will speedily become clouded from tho water escaping from the grass. Even in tho driest seasons, if a cold bellglass be placed over growing grass, water enough to trickle down the sides of the glass will be deposited in a few minutes. An acre of grass exhales a large number of hogsheads of water in a day. Great masses of any foliage give off great quantities of water daily, and prevent stagnation. Most plants that farmers cultivate uso up over two hundred times their dry weight of water. A single plant of barley, in full growth aud vigour, requires the passage through it, while in the soil, of more than a gallon of water. An aero of cabbages, in full growth, will use more than ten tons of water in twelve hours. _ It is very evident, then, that if water in, large quantities bo not available for growing plants, their growth and development are stunted, and imperfect crops, rcsultiug in serious loss, is tho conscqucnco. The evaporatipn of tho water from the leaves keeps tho plant cool, even in tho hottest weather. Absence of Sunlight and Heat. If a plant, thus constructed and nourished, bo placed where it cannot receive sunlight and heat, it -becomes of a sickly white colour. During the process of manufacturing and oxidising plant food in the plant laboratory, a certain amount of heat is evolved by the oxidation within tho plant, but that heat will not prevent tho plant, in the absence of sunlight, from losing its colour, liut if placed whero it can rcceivo sunlight, it quickly presents a healthy and vigorous appearance, and becomes, while growing, mostly of a green colour. The sunlight acts on the carbonic acid in the leaves, and produces carbon, without which no green plant can grow. Tho foliage of young plants cannot oven exist for ' any length of time when exposed to sunlight in air that ■is totally l'reo from carbonic acid. Carbonic acid enters the leaves very much as the liquids enter the roots. The amount of carbonic acid decomposed depends on the intensity of the light; and the prosperity of the plant depends largely upon the amount of light it receives. When a ray of sunlight passes through a three-sided piece of glass, it is found to consist of a number of differently-colourcd rays. When tho sunlight enters the leaves or tho flowers of plants, tho particles of which the leaf or the ilower is formed act on tho sunlight exactly as tho three-sided piece of glass actcd. The ray is resolved into, the different-coloured rays of which it was composed, one of the rays being , reflected to the eye of tho observer, and the ■remaining rays absorbed by the plant. If the red ray be reflected, the leaf or the flower will appear of a red colour; if the green rav be reflected, the colour of the leaf or the flower will be green. ' In this way sunlight colours the grass, the leaves, and the ilowers. But tho sunlight (locs more than produce colour: The sunbeam contains heat rays, in addition to the rays' of colour. These heat rays, in conjunction with the carbonic acid gas, act on the plant food, and, chiefly in the day time, convert, or help to convert, the plant-food into starch. Largely in the night time, the starch is converted into sugar, aud other nourishing substances, and sent to all parts of the living, healthy plant, to nourish it. If a plant, thus produced from a seed, ■be placed on a red-hot plate of iron, most of it will vanish into air, and a small part, the ash, will remain on the plate. If a growing plant of a hundred pounds in weight be burnt, it will usually be found that 95 pounds will- thus vanish, and only about five pounds of ashes will remain on tho plate. The organic part of the plant which vanished consists chiefly of woody fibre: starch, sugar, gum, oil, and fat. The inorganic part of the plant consists mostly of lime, magnesia, potash, soda, iron, manganese, sand, iodine, and various acids. It thus appears that plants consist of the ordinary gases of nature, and the ordinary substances of the soil. Wo shall endeavour to show how all these substances find their way into the organisation of the plant. The presence of moisture in tho atmosphere alone is of little avail for the successful growth of crops. The vapour must be condensed, fall iu rain, aud penetrate the soil. Tho tliroo chief condensers are: (a) trees and forests, (b) hills and mountains, (c) cold derived from any source. Many instances could bo given, such as at Honolulu and Trinidad, whero forests originally existed, and until these wxsre cut down, the rainfall was sufficient and regular. After tho forests were cut down, the rainfall largely decreased, and the rain fell at irregular intervals. No sooner had trees been extensively grown again, than the rainfall again increased in quantity, and became more regular. In Now Zealand, mountains and forests condense the vapour in tho province of Westland, and a rainfall of from 92 to 115 inches or more is the result. In tho province of Auckland, these condensers aro largely absent, and the consequence is a low rainfall of from 3G to 53 inches yearly. In Australia a range of mountains runs roughly parallel with the east coast line, and usually at 6ome distance inland. Between tho mountains and tho coast line tho rainfall is high-and regular, while on tho vast plains of tho interior it is low and irregular. Whero cold air currents exist, whether the result of permanent atmospheric conditions, or indnced by the prosenco of large sheets of water, then the inlluenco of such conditions in contracting the air, aud hence causing it to precipitate its vapour in the form of rain, is great aud apparent.