March 17, 1870. ] 



JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 



207 



were proved that the plant could absorb and assimilate it in an 

 nncombined state from the air, it would at once determine the 

 question of the value of nitrogen as an ingredient in manures, 

 as it would be clearly unnecessary to add more. 



Let us examine, then, the grounds on which it is stated that 

 nitrogen cannot be taken into the plant directly from the air. 



First, I would call attention to the fact, that nitrogen is the 

 most inert of all substances. It is colourless, tasteless, in- 

 odorous, and chemically the most inactive of all elements. 

 The most important purpose it fulfils, is to dilute oxygen ; it 

 acts, in fact, just the part that water does to alcohol, dilutes 

 the stimulant, as a man takes water to his brandy. Alcohol in 

 its pure state is a violent poison. If only the proportion of 

 oxygen in the atmosphere were increased i or 5 per cent., it 

 would act as too great a stimulant to the lungs, and we should 

 die from combustion ; so, too, though nitrogen is not directly 

 poisonous, yet the life of neither plants nor animals could be 

 supported in it. Put an animal under a bell-glass filled with 

 nitrogen only, it perishes in a few minutes. It was from this 

 cause that chemists gave it the name of Azote — a non- sup- 

 porter of life. 



Again, so little is nitrogen necessary for the well-being of a 

 plant, that most of the principal vegetable Bubstances, as starch, 

 gum, and sugar, contain no nitrogen at all. Instance the 

 following— C, being carbon ; H, hydrogen ; 0, oxygen. 



Cellulose.. C. 24 H. 21 O. 21 | Mucilago .. C. 24 H. 20 O. 20 



Starch C. 24 H. 20 O. 20 Cane Sugar C. 24 H. 18 0.18 



Dextrin . . C. 24 H. 20 O. 20 | Grape Sugar C. 24 H. 22 O. 22 



all of which, it may be observed, consist merely of carbon and 

 water. But even in those vegetable substances in which it 

 does exist, its proportion is very small as compared with that 

 of any other of the elements. Take for intance the following 

 analysis, according to Professor Johnstone, of Wheat, both 

 grain and straw, hay, and Turnips. 



And this, too, it must be borne in mind, after the substanoes 

 have been artificially dried. In the growing crops the pro- 

 portion of nitrogen is much less, as the water in the above 

 analysis which forms so great a bulk of all growing crops, has 

 been artificially abstracted. So great is the bulk of water in 

 some crops, that it forms 80 to 90 per cent, of the weight of 

 Turnips ; Potatoes from 60 to 80 per cent. ; grass from 40 to 

 50 per cent. So that in the case of Turnips, nitrogen which 

 only forms 1.7 per cent, of the dried root would form .24, or 

 about one part in 400 of the growing root. 



An examination of the foregoing analyses will prove that 

 even where nitrogen does exist in plants, it bears a very small 

 relative proportion either to carbon or oxygen, and as a rule 

 plants contain nearly three times as much hydrogen as ni- 

 trogen, evtn in their dry state, that is artificially dried at a 

 temperatme of 212°, till all water is evaporated; and when 

 compared to hydrogen in plants in their growing state, ni- 

 trogen bears a very small proportion indeed, as the sap of all 

 plants is water containing certain ingredients in solution, and 

 water contains equal parts of hydrogen and oxygen, conse- 

 quently in all growing crops the quantity of hydrogen is much 

 greater in proportion to the nitrogen than when the plant is 

 dried. 



We see, then, that nitrogen plays a very unimportant part 

 in the economy of a plant, and it seems to me to be contrary 

 to all the provisions of nature to place a plant in a medium 

 necessary to its existence, and yet that the plant should not be 

 able to assimilate from that medium what it requires. Yet 

 that is the line of argument which those persons must take 

 who say that, though the quantity of nitrogen in a plant is so 

 small, yet, though it exists in an atmosphere containing 78 per 

 cent, of it, it cannot take what it requires from it. And it is 

 not true in any other case, for in no other instance are plants 

 placed in a medium which is necessary for their existence 

 without their having the power of assimilating it. Moreover, 

 however much of any one substance may surround the plant, 

 yet it will never take more of it than what it requires, as all 

 plants have the power of selecting the ingredients which are 

 necessary to their welfare. This is very remarkable in com- 



paring the different mineral ingredients of the ashe3 of plants, 

 one being rich in silicon where another is rich iu potash or 

 soda, and so on. So, too, though carbon is present as carbonic 

 acid only in the proportion of one part in 2500, yet plants take 

 as much or more weight of carbon from the air than oxygen, 

 which is a fifth part of the atmosphere. So there is no proof 

 that plants cannot take nitrogen from the air by saying that if 

 they could there would be more nitrogen found in them. The 

 only reason is that it is not necessary to their existence to 

 have more. 



One argument is that no elements are taken np from the air 

 in an uncombined form. Let us see how far this holds good. 

 There are only two elements presented to the plant from the 

 air chemically uncombined, and those are oxygen and nitrogen, 

 and it is a well-ascertained fact that plants absorb and assimi- 

 late the oxygen ; so that out of the only two pure uncombined 

 elements to be found in the air, actual experiments have proved 

 that the plant does assimilate one of them, which certainly, to 

 say the least, weakens the argument in the case of the other. 



Let us see, then, what is the case with the other constituents 

 of the air. Carbonic acid is one part of carbon combined with 

 two parts of oxygen, and is generally represented by the for- 

 mula COo. It is perfectly unnecessaiy for me to state what 

 is so well-known a fact, that one of the principal sources of 

 carbon to plants is what is absorbed by their leaves in the form 

 of carbonic acid. Again, another ingredient in the air is 

 aqueous vapour ; this varies from day to day in quantity ac- 

 cording to the hygrometrical condition of the atmosphere, but 

 all gardeners know that plants are capable of absorbing this 

 aqueous vapour by means of their leaves. Take, for instance, 

 the case of a plant flagging in a house from hot sun ; if water 

 is thrown upon the floor and stages, and the air charged with 

 aqueous vapour, the leaves will absorb it, and soon regain their 

 original condition without any water being applied to the root. 

 Ammonia, again, which is found in very small quantities in 

 the atmosphere, can also be taken in as food for plants through 

 their leaves. This has also been found by actual experiment, 

 by increasing the quantity of ammonia by evaporating car- 

 bonate of ammonia or other ammoniacal salts in the air of a 

 large glass receiver, and putting the plant into it. Oat of five 

 substances, therefore, presented to the plant in the air, four of 

 them are known to be assimilated a3 food. Why not the fifth, 

 which forms the greatest bulk of all in the atmosphere 1 



There is so small a quantity of nitrogen in plants, that any 

 experiments to prove that plants absorb or do not absorb nitro- 

 gen from the air are attended with great difficulties, and many 

 sources of error. For instance, all water is charged with air, 

 and therefore nitrogen is presented to the roots of plants in 

 the water they absorb; again, all soil that has had animal or 

 vegetable manure decomposed in it eontains nitrogen, and all 

 rain water contains nitrogen in the form of ammonia ; so that 

 it would be very difficult, or almost impossible, to keep a plant 

 growing so that it could obtain its nitrogen from the air alone. 

 It is chiefly owing to these difficulties that accurate experi- 

 ments have not been made. 



Those who assert that nitrogen cannot be absorbed as food 

 from the atmosphere say that the plant takes up all its nitrogen 

 from ammonia which supplies the nitrogen in a combined form 

 as N H s , one part of nitrogen to three of hydrogen, or else by 

 nitric acid. Now, all the compounds of nitrogen are exceed- 

 ingly unstable — that is to say, whenever nitrogen enters into 

 combination with other elements it has no powerful affinity 

 for any element at all ; nitric acid, or five parts of oxygen to 

 one of nitrogen, being, perhaps, the most stable of any. It is 

 this property of nitrogen which forms the explosive quality 

 of most of its combinations, as in gunpowder, gun cotton, 

 &c. It is this which makes nitro-glyceriue so dangerous a 

 compound ; but, dangerous as nitro-gljcerine is, there are 

 other combinations of nitrogen more dangerous still. If, for 

 instance, chlorine gas is placed in a glass receiver, and held 

 over a solution of ammonia, oily-looking drops are seen to 

 form on the surface of the liquid, and will fall to the bottom. 

 This substance is chloride of nitrogen, and will explode evea 

 under water if it be only touched with anything in the least 

 greasy, as a glass rod dipped in oil. Again, if iodine be droppel 

 into a solution of carbonate of ammonia, a grey precipitate is 

 formed ; if this be collected by means of filtering it through 

 blotting-paper, and dried, the powder is so powerfully explosive 

 that merely shaking the paper or the slightest touch will ex- 

 plode it, and it can never be made, except in the smallest quan- 

 tities for the sake of experiments. 



Now, though ammonia, N H3, is one of the most stable forms 



