600 



THE IRRIGATION AGE. 



Proportions of the Foregoing Elements in Plants. 



Although the substances of plants are composed 

 mainly of the above organic elements, they exist in very 

 different proportions. This will appear from the follow- 

 ing table of "dried" plants, taking one thousand parts by 

 weight as the standard: 



Oats. Cloverseed. Grass, hay. Peas. Wheat, Potatoes. 



Carbon 507 494 458 465 455 441 



Hydrogen 64 58 50 61 57 58 



Oxygen 367 350 387 401 431 439 



Nitrogen 22 70 15 42 34 12 



Ash 40 28 90 31 23 50 



1,000 1,000 1,000 1.000 1,000 1,000 



The above proportions are slightly variable, but the 

 figures given represent nearly the relative weights in 

 which these elementary elements enter into forms of vege- 

 table matter. Herbaceous plants generally leave more ash; 

 that is, inorganic matter, the wood of trees and the differ- 

 ent parts of plants yielding unequal quantities. 



How Organic Elements Combine to Form Plant Foods. 



Carbon being a solid and insoluble in water, cannot 

 be taken up through the pores of the roots of plants, the 

 only parts with which it can come in contact. Hydrogen, 

 in its simple state, forms no part of the food of plants 

 because it does not exist in the atmosphere or in the soil 

 in any appreciable quantities. Oxygen exists in the at- 

 mosphere in the gaseous state and may be inhaled by the 

 leaves of plants. Nitrogen may be absorbed by the leaves 

 of living plants, but in a quantity so small as to escape de- 

 tection. Moreover, oxygen and nitrogen being soluble 

 in water to a slight degree, may also be absorbed in small 

 quantities along with the water taken in through the pores 

 of the roots. 



But this absorption by the plant is insufficient to main- 

 tain its life and growth. It must have a liberal supply 

 of food in which the four elements specified form a large 

 percentage. Now, this food can only be obtained, or man- 

 ufactured, by the four organic elements entering into mu- 

 tual combinations to form what are known as "chemical 

 compounds." It is these chemical compounds which find 

 their way into the interior of the plant, into its very sub- 

 stance, and then the plant grows and reaches maturity, 

 provided these chemical combinations are continued during 

 its period of existence. 



It must be borne in mind that the atmosphere diffuses 

 itself everywhere. It makes its way into every pore of the 

 soil, carrying with it its oxygen, carbonic acid and other 

 substances it may be charged with, to the dead vegetable 

 matter and to every living root. Its action is double play- 

 ing among the leaves and branches, and fondling the roots 

 by mingling with the soil. It is the workman, and its 

 tools are its gases, and with them it manufactures out of 

 the raw material it finds in the soil that is, the silica, the 

 sulphur and other inorganic substances, and the decayed 

 organic matter -chemical combinations which the plant 

 seizes, appropriates and digests. 



Chemical Combinations. 



When common table salt and water are mixed the 

 salt dissolves and disappears. By evaporating the water 

 it is possible to recover the salt in the same form and con- 

 dition as it was at first. This is called a "mechanical 

 combination," with which chemistry has nothing to do, 

 and which would not, in the economy of nature, be suffi- 

 cient as a plant food, although such combinations and 

 solutions are absorbed by the plant they do not feed it! 



But when limestone is put into a kiln and burned it is 

 changed into an entirely different substance, which is 

 called "quicklime." The limestone is decomposed by the 

 burning, the carbonic acid mixed with lime is driven off 

 by the heat and lime remains. 



So when sulphur is burned in the air it is all converted 

 into a white vapor of an unpleasant odor, which is finally 

 absorbed by the atmosphere and disappears. This is also 

 a chemical decomposition, in which the sulphur is com- 

 bined with the oxygen of the atmosphere. 



To cite another illustration, it may be said that water 

 itself is a chemical compound of the two elementary 

 bodies, oxygen and hydrogen. 



None of these latter are mixtures like the mixture of 



salt and water, but elementary bodies united to form new 

 substances, which, as has been said, are called "chemical 

 compounds," and it is through these chemical combina- 

 tions that all plants and fruits possess their various pecu- 

 liarities. 



The number of compounds which the four organic 

 elements form with each other is practically unlimited, 

 but of them a very few only minister to the growth and 

 nourishment of plants. Of these water, carbonic acid, am- 

 monia and nitric acid are the most important. These com- 

 pounds we shall take up in their order, a knowledge of 

 all of them being of essential importance in agriculture. 



Water. 



The following are the three qualities of water impor- 

 tant to plant life: 



First A solvent power. 



Second An affinity for certain solid substances. 



Third An affinity for its own elements. 



First Water possesses the power of absorbing the 

 several gases of which the atmosphere is composed, and 

 carries them to the roots of plants whence they are taken 

 into the circulation. 



It dissolves many solid inorganic substances, earthy 

 and saline, and conveys them in a fluid form to the roots 

 of plants, which enables them to ascend with the sap. It 

 also takes up substances of organic origin, such as por- 

 tions of decayed animal and vegetable matter, and likewise 

 brings them within reach of the roots. 



When warm the solvent powers of water over solid 

 substances is very much increased, a fact which accounts 

 for the luxuriant vegetation in the tropical and semi-tropi- 

 cal regions, and in what are known as "warm soils." 



Second Water exhibits a remarkable affinity for solid 

 substances. A familiar instance is mixing water with 

 quicklime. The lime heats, cracks, swells and finally be- 

 comes a white powder. This is familiarly known as "slak- 

 ing" lime. When thoroughly slaked, the lime will be found 

 to be one-third heavier than before. Every three tons of 

 lime, therefore, absorb one ton of water; hence, if four 

 tons of slaked lime is put upon land one ton of water is 

 also mixed with the soil. 



Water has an affinity for clay, the hottest summer 

 seldom robbing the clay of its water, enough being re- 

 tained to keep wheat green and flourishing when plants 

 on lighter soils are drooping and burning up. 



An affinity for water causes vegetable matter to com- 

 bine chemically with it, but in the case of a porous soil 

 the water is merely "drunk in" mechanically and it is re- 

 tained unchanged in the pores of the soil, whence it may 

 be evaporated out, but not where there has been a chem- 

 ical transformation. Thi?, is a fact that should be re- 

 membered in applying mixtures of vegetable matter to 

 the soil by way of fertilization. A mere mechanical mix- 

 ture is of little effect; there must be a chemical trans- 

 formation provided for. And it should also not be for- 

 gotten that water itself is capable of a chemical change 

 whereby its qualities are preserved and retained much 

 longer, indeed, than if merely poured upon the soil as a 

 mechanical attempt to assist plant growth. 



Third Water possesses an affinity for its own ele- 

 ments, and this fact exercises a material influence on the 

 growth and production of all vegetable substances. In 

 the interior of plants, as in animals, water undergoes con- 

 tinual decomposition and recomposition. In its fluid state 

 it finds its way into every vessel and every tissue. In this 

 situation the water yields its oxygen to one portion of the 

 plant and its hydrogen to another portion, wherever either 

 is needed, and, in like manner, the oxygen and the hydro- 

 gen resume their combination as water and cling together 

 until a new chemical change is needed. To comprehend 

 this better the reader has only to observe the effects of 

 water on his own system, for, as between plants and ani- 

 mals, the transmutations of oxygen and hydrogen, con- 

 veyed into the system by means of water, are practically 

 identical. 



Carbonic Acid. 



Carbonic acid, as has been said, is the gas from burned 

 charcoal, or carbon. It has an acid taste and smell, is 

 soluble in water and reddens vegetable blues. Water dis- 

 solves more than its own bulk of this gas. It is only one- 

 half heavier than atmospheric air, and is deadly in its 

 effects. Yet it is the principal food of plants, being ab- 



