Agriculture.

Poverty Bay Standard, Volume XI, Issue 1260, 27 January 1883, Page 2 (Supplement)

Agriculture.

HOW PLANTS GBOW.—No. 1. By B. W. Emebsos Maclvob, F.1.C., F.C.S. Ac. AUTHOR OF “ THE CHEMISTRY OF AGRICULTURE.” GERMINATION. A perfect seed contains in a concentrated form all the nutriment required to feed the germ till the root and leaf are formed. In one class of seeds, of which the cereals are examples, starch is the most abundant constituent, whilst in another class of members, this substance does not exist, but in its place there is a large proportion of fat. All seeds contain albuminoids, and their ashes are rich in potash and phosphoric acid. It is important that agricultural seeds should be thoroughly matured in growth, as otherwise they will be deficient in one or other of these essential constituents and this deficiency will be manifested by the weakness of the plantlets produced from them. Hence the farmer should be careful in selecting only the best of his grain for sowing purposes. In order that seed may germinate properly, it is essential that atmospheric air should have ready access to it, and also that certain conditions of warmth and moisture should exist in the soil. Under these conditions the seed absorbs moisture and oxygen, which latter by acting upon some of the carbonacious substances produces carbonic acid. The chemical changes that take place are numerous and highly interesting. At first, a small proportion of the albuminoids is changed into a substance termed diastase, which converts the insoluble starch and fat into sugar, the albuminoids into soluble amides and other compounds, with the food thus rendered available, the radicle or root and the plumule or shoot are nourished ; they increase in size, force their way through the skin of the seed, and, provided the soilconditions are favorable, at once commence to assimilate food from the soil and atrdosphere respectively. The malting of barley or other grain is an opera tibn in which the process of germination is conducted on a very extensive scale. The seed is allowed to germinate, and the embryo plants to develope considerably when they are killed by exposure to a heat of from 145 deg. to 160 deg. Fahrenheit, according as the malt is required to be light or dark in colour. Changes identical to those which go on in seed when in the soil take place when it is treated in the malt-house. Diastase is developed and converts the starch into sugar Ac. It is said that one part of this substance will render soluble 2000 parts of starch, and, as a large quantity of it remains until the last stage of the malting, the distiller is enabled to ferment molasses or starch or unmalted grain by mixing with them from 10 to 15 per cent of malt. Seeds should not be sown too deeply as they may not germinate, owing to want of oxygen ; or, if they do germinate, the shoot may be unable to force its way to daylight before the supply of food in the seed is quite exhausted. It is a general rule that the smaller the seed the nearer to the surface it should be sown. Efforts have been made by both scientific and practical men to hasten the germination of seed by chemical and other means. It is proposed by Bollger to soak the seeds in a fairly strong solution of caustic potash or soda, but the results are found to be unsatisfactory. Chlorine gas dissolved in water is also recommended, and, in some instances, has acted moderately well. Camphor is said to exercise a wonderful effect in promoting the process without hurting the seeds. However, very little is to be gained by treating ordinary farm seeds in either of these ways. Having thus briefly noticed the subject of germination, and traced the growth of the plantlet till it begins to get food from external sources, we may proceed to discuss the general structure of plants, and the functions of their leaves and roots. THE VEGETABLE CELL. A plant is composed of minute bags or cells lying closely together. These are filled with i nitrogenous substance termed protoplasm, which is held to be the most elementary principle found in living objects, or, in other words, the material from which all structures —whether vegetable or animal—are developed. From this protoplasm new cells are produced in growing plants. In shape the so-called ' primary cell is globular, but circumstances rften alter it considerably. It varies not only n different plants, but in different parts of .he same plant. In cotton and hemp the cells ire long and thin, whilst in other cases they ire spheroids. The size of the cell also varies rery much. In fungi, such as the red-rust of vheat, they are not more than l-5000th of an nch in diameter, whilst in some marine flants they are a foot in length ! As a rule, lowever, cells are very minute. The walls or nvering of the cells consist of cellulose composed of carbon and the elements of rater, viz., hydrogen and oxygen), are elastic .nd permeable to both liquids and gases. )n examination the cell is found to contain jreen coloured corpuscles, (chlorophyll) starch, ugar, and salts, in addition to the nitrogenous übstance already mentioned. By careful uicroscopicai inspection, fat is also found, n the form of minute particles, surrounded y the protoplasm. These latter play an imortant part in the production of new cells. l particle divides itself into moieties, each of rhich is walled in by the nitrogenous principle ro topi asm. Thus cells increase or multiply y division. This growth is often very rapid, s may be judged from the fact that a variety f puff-ball said to produce three or four inndred millions per hour. The development f the rust fungus is also surprisingly great. True cellular tissue, consisting of the ordinary globular cells only, is found in sea-weeds nd other varieties of the lower class of plants. Voody-tissue is composed of long and slender ells, overlapping each other, whilst vascular issue is formed by the union of simple cells, nd of woody cells. The latter occurs in traw and the stems of grasses, Ac. Several ther kinds of cells are recognized by physioigists, but they need not be noticed here. FUNCTION OF THE LEAVES. The structure of an ordinary leaf is easily bserved by the aid of the microscope. The urface is seen to be studded over with small ores of mouths [stomata] which vary in umber and size according to circumstances, ome leaves have as many as 160,000 pores er square inch, whilst others possess only 00, or even less to the same surface. In eneral the leaves of plants growing in damp nd sheltered situations are found to have not nly le largest sized, but also the greatest umber of stomata. The pores are most umerous oh the underside of the leaf, and ley >ossess the remarkable property of using in dry air and opening in moist. An important function of leaves consists in le transpiration of water. This process consts in the escape, or rather the evaporation I water from within the body of the plant trough the pores of the leaves. The trans[ration proceeds through the stomata on the nder part of the leaves, and only in light, is not completely stopped by the atmosnere becoming saturated with moisture, ) long as the plant has plenty of suntine. Evaporation may go on to a small [tent in darkness, but this is attributable to tother cause than the one under notice. The nount of water carried off in this process is sry large. Mr. (now Sir John) Lawes, has town that wheat, oats, barley, beans, peas, id clover, exhale, during five months growth, r er 200 times their dry weight of water! rom this it is easy to understand why land tat has borne a crop is much drier than a tked fallow. The mount of water exhaled r plants is of course influenced by local cirtmstances. When the ah is dry and warm le evaporation is very rapid; and if water capes by the leaves quicker than it is worked by the roots, the plant will wither, id may even die. In moist dull weathrr le process is very slow, and sometimes alost stops. It is well known that potatoes rown in a wet shaded place are watery and efieient in starch. This result is due to the inctions of the leaves being interfered with. The evaporation of water from the leaves of lants is the main cause of the circulation of le sap, and the absorption of water from the )il containing in solution the mineral conlituents of plant food and also the nitrogen.