IRISH GARDENING 



59 



The Food of Plants. 



By Chemist. 



Carbon, more than any other element perhaps, 

 looms large hi interest and. importance in the eyes 

 of the chemist. In the uncombinecl state, as in 

 the naore or less pure forms of charcoal, coke, 

 soot, smoke, &:c., it cannot lay claim to any 

 special distinction ; though this is far froni being 

 the case when the element ])asses into the pure 

 crystalline form of d.iamond. Thereupon, like 

 Cinderella in the fairy tale, it comes forth froni 

 obscurity and outshines in splendour all com.- 

 l)etitors. In the realm of chemistry, however, 

 the great interest and importance of carbon lies 

 in its wonderful power of combining with other 

 t'lements to form coiiqxjunds almost without 

 uuihIkt. Aiii(iiil,s1 tlusc compounds are to be 

 fnuiul the various iinnlucts of animal and vege- 

 table life, the iutt-rt sting and often highly complex 

 substances that build, up living tissues, into the 

 composition of whicli carbon enters in every 

 case ; and thus the element in its close association 

 witli life, possesses an interest for the zoologist 

 and botanist no less than for the chemist. 



Another element closely associated with life is 

 nitrogen. It does not enter into the composition 

 of vegetable substances to the same extent as 

 carbon does, there being none for instance in 

 starch or sugar, in cellulose, in wood, in fibre, 

 bark. A;c. But its presence in the protoplasm, in 

 the u,ii'e)i colouring matter, in the jjollen, and in 

 111!' allnimen food store in the seed, gives an in- 

 iliration of the vital importance of nitrogen in the 

 economy of the plant. Unlike carbon, nitrogen 

 is mighty slow to enter into combination ; but 

 once it does combine with other elements the 

 compound is usually of outstanding im])ortance. 

 This fact is well enaphasised hy a distinguished 

 American professor writing in Harper's Magazine : 

 " The romantic deportment of the nitrogen atom 

 is fascinatingly interesting to the student of 

 chemistry. Wherever he looks he sees at once 

 that nitrogen is the most restless, the most 

 powerful of the elements. . . . Entering into 

 combination with a few other atoms it will yield 

 us the most delicious perfumes, while it is equally 

 ready to join forces with others to produce sub- 

 stances whose smell of utter vileness has the 

 psychological effect of causing the ex])erimenter 

 to ' wish he were dejul.' In t be aniline dyes it 

 enhances our clotliing with a tbousaiul l)eautiful 

 coloui-s, and in still another thousand forms it 

 enters the chanxbers of the sick in the healing 

 gviise of all the synthetic medicines. It lurks in 

 ))russic acid, in the ]:)tomaines, and in a host of 

 (leadliest poisons. It drives our bullets in the 

 form of gunpowder, it explodes our mines as 

 dynamite and gun-cotton. . . . We have been 

 accustomed in the past to ascribe to carbon the 

 role of life-element paran^ount ; b\it the more the 

 question is studied, the m.ore does it appear 

 evident that the carbon constituent of the body i'^ 

 the mere brick and mortar of it, good, erunigh to 

 burn as fats and carbohydrates to nuiintain the 

 fires, but the working vital thing is the restless 

 versatile nitrogen. . . . And yet this nitrogen, 

 so energetic when combined with other elements, 

 is in its carefree solitary condition, a stubborn 

 lazy inert gas, chenxically s|)eaking, all Init un- 

 alterable and. unco mbinable. The ' all but,' how- 

 ever, is vastly important." 



We may take i, . therefore, that nitrogen is a 

 very important element in the food of plants. 

 Curiously enough the source from which the 

 plants derived it was for a long time a matter of 

 very keen controv^-rsy. By some scientists the 

 view was held that ])lants were able to assimilate 

 the free nitrogen of the air, something after the 

 manner in which they assimilate carbon. If, for 

 instance, the water within the leaf should be 

 split up and its hydrogen combined with the 

 nitrogen of the air present in the ])ores of the leaf, 

 there is formed the com^jound ammonia : or if the 

 oxygen of the water be combined instead- tbeii 

 nitric acid is produced- Either com])ou?id might 

 be looked upon as the first stage in the assin-ila- 

 tion of nitrogen. Why not call upon the sunlight 

 to accomplish the work? If its aid could be 

 invoked to assimilate carbon it was natural to 

 think the same boundh ss source of ener<r\ could 

 be drawn upon for tbe assimilation nl' (iitr.r_cen. 

 Some such synthesis seemed, highly prohahle Irom 

 the fact that combined nitrogen rarely if ever 

 occurs in the rocks from which soils are formed 

 by weathering. Its presence now in the soil 

 points to some combining agency being at work. 

 As for those naturally occurring beds of nitrate 

 and other nitrogen compounds, which are to be 

 found in certain rainless districts, it is generally 

 held, that these are of organic origin, due to tl)'e 

 activity of life of some former period, and not to 

 the decay of underlying rock. The same natural 

 agency that formed theje nitrates may be 

 assumed to be actively at work to-day. 



It must also be borne in mind that animals 

 obtain their nitrogenous food from the plants on 

 which they feed. : from the grass, corn, roots. \r.. 

 in the case of farm anima's. Now, the question 

 arises, what made good the loss of combined 

 nitrogen due to the sale of cattle, cheese, and 

 other conamodities from off the land, a loss whi<'h 

 must have been going on for centuries and 

 centuries prior to the introduction of artificial 

 manures and foreign feeding stuffs ? From such 

 considerations it was clear there must be some 

 natural agency at work, combining the free 

 nitrogen of the air, and in the absence of any 

 more rational explanation, then' was at least a 

 strong ]iresum])tion that this all-imi)ortant office 

 was fulfilled by green plants through their jHtwer 

 of utilising the energy of the sun. 



On the other band." if i)lants could thus make 

 use of the free nitrogi-n of the air, one very 

 common practice in the growing of crojis would 

 lose its meaning. There should be no need for 

 the application of nitrogenous manures. But we 

 know how readily crops resijond to such treat- 

 ment. One might imagine that cabbage, i)ota- 

 toes, niangolds, &c., with their great develo])- 

 ment of leaf surface, would possess s])ecial 

 facilities for utilising sunlight in the assimilation 

 of nitrogen. But it is useless to try to grow these 

 crops successfully in soil iioor in nitrr)gcnous 

 material- Any hoi)e that the nitrogen of the air 

 will make good is an illusion. This is the common 

 experience in the cult ivati(Ui of the land — an ex- 

 ])erien< (' which is further conlirnucl l)y the testi- 

 mony of specially arranged exjieriments carried 

 out in the laboratory. 



An experiment of the kind carried out more 

 than half a century ago may be worth recalling 

 now, inasmuch as it takes us back to the re- 

 searches of Bous.siugault (Professor of Agricul- 

 tural Chemistry, Paris), who devoted special 

 attention to the question of nitrogen assimilation. 



