42 



THE FARMER'S MONTHLY VISITOR 



Marofi, 1842. 



based on an exact acqiuiinlance with the means 

 of niitriiion of vesceiahles; and with llie influ- 

 ence of soils and the action of manure upon 

 them. This kiiowledjie we must seek from 

 chemistry, uhicli teaclies tlie mode of investiga- 

 ting the'coin|iosition, and of studying tlie char- 

 acters, of the different substances from which 

 plants derive tlieir nourishment." 



"Innumerable are the aids afforded to the 

 means of life, to manufactures and to commerce, 

 by the truths which assiduous and active m- 

 quirers have discovered and rendered capalile of 

 jiraclical application. But it is not the mere 

 practical utility of these truths, which is of nn 

 portance. Their influence upon mental culture 

 is most beneficial ; and the new views acquired 

 by the knowledge of them enable the mmd to 

 recognise in the phenomena of nature proofs of 

 an infinite wisdom, for the unfathomable profun- 

 dity of which human language has no expres- 



The work is devoted to an explanation of the 

 proper food of plants, and the modes in which, 

 and sources from which they receive this nour- 

 ishment. Connected with these matters, come, 

 of course, the value and uses of manures, and the 

 true art of culture. These subjects are all ob- 

 viously of the highest importance; and it is ex- 

 ceedingly interesting to see how a nfmd so pow- 

 erful and learned discusses them. The author 

 speaks with just respect of that distinguished 

 man, the late Sir Humphrey Davy, who first 

 taught systematically the application of chemical 

 science "to agriculture ; and he shows himself not 

 an unworthy pu[iil of so eminent a master. We 

 can do but imperfect justice by an abstract of his 

 views; yet it is all for which we have room. 



The elements or constilnet-.ts of all plants are 

 carbon, water, (or its elements, hydrogen and 

 oxygen,) nitrogen, and some earthy or alkaline 

 salts. The food of plants can be received only 

 in a gaseous or soluble form, and it must come 

 from the atmospheie, from the earth, or from 

 both. No earthy substance can ever be received 

 into a plant indess in a dissolved or coudiined 

 state ; and though crude substances, incapable 

 of assimilation, may in some cases be taken up 

 by the roots of the plant, which seem to have no 

 power of selection in regard to their food, yet 

 they will he exuded from the roots in the s^tateir 

 which tliry were received. The alkaline sub 

 stances received and assinfilated by plants car 

 only be ascertained by iheir ashes alter incinera- 

 tion, and consitute a very minute portion ; but 

 however nfnnite, they are evidently essential to 

 the perfection or nuctification of the plant. Be 

 sides these there are certain organic acids, 

 which are found in the juices of plants and usu- 

 ally combined with some inorganic Iwses. The 

 alkaline bases or earths must exist in the soil, or 

 they cannot be found in the plant. In some 

 cases, however, one kind may be substituted for 

 another. 



The author discusses at large the doctrine of 

 humus, humin, ulmin, humic acid, apotheme, 

 geine, all referring to one substance, as the food 

 of plants. This matter is generally understood 

 to be a certain brown or carbonaceous substance 

 resulting from vegetable decomposition. Some 

 portions of it are soluble in water or alkalies; 

 other portions are insoluble but by extraordinary 

 means. The common opinion has been that it 

 constitutes directly the food of plants, and 

 quires only to be dissolved to be taken up by the 

 roots of the plants and assimilated by them. 

 Others have maintaiiied that it requires to be 

 dissolved by the application of alkalies, and com- 

 bining with them in the form of an acid, it be- 

 comes then prepared for the food of plants. — 

 Our author wholly denies these positions by 

 showing that so far from humus being extracted 

 from the soil, it is in f;ict increased by cultivation, 

 as in the case of a forest, the more abundant the 

 growth of wood upon it, the greater the amontit 

 of humus in the soil, where the debris of the 

 wood is suffered to remain upon the land. 



'•A certain quantity of carbon is taken ever 

 year from the forest or meadow in the form o"f 

 wood or hay ; and, in spite of this, the quantity 

 of carbon in the soil augments; it becomes rich- 

 er in humus." — p. 68. 



"The opinion that the substance called humus 



sues, is so general and bo firmly established, that 

 hitherto any new argmnent in its favor has been 

 considered unnecessary ; the obvious difference 

 in the growth of plants according to the known 

 abundance or scarcity of humus in the soil, 

 seemed to afford incontestable proof of its cor- 

 Yet this position, when admitted to a 

 strict examination, isfoiuid to be untenal)le: and 

 it becomes evident that humus in the form in 

 which it exists in the soil does not yield the 

 smallest nourishment to plants." — p. 61. 



He attempts to prove his position, that the car- 

 bon of the plant cannot be derived from the soil, 

 by a calculation in weights and measures. Humic 

 acid, or the humus of the soil, can only be ab- 

 sorbed by the plant in combination with some in- 

 ganic bases or metallic oxide. VVe do not think 

 it important here to give anything more than the 

 results of some of his calculations. Ue suppo- 

 ses that upon an average 40,000 square feet of 

 land, Hessian measure, yield annually 20.50 lbs. 

 of dry fur wood, which contains 5.6 lbs. Hessian 

 of metallic oxides. Now it is ascertained in what 

 proportion humic acid combines with the metal- 

 lic oxides, with lime for example. Having deter- 



iied the metallic oxides existing in such a pro- 

 duct, he easily determines the amount of humic 

 acid thus introduced into the trees; and allowing 

 humic acid to contain 58 per cent, of carbon, this 

 would correspoiul only to the production of 91 

 lbs. Hessian of dry wood. But 2050 lbs. of fir 

 wood are actually produced. These calculations 

 are well worth e.xamining, and, if accurate, it is 

 difficult to deny the inference which lollows from 

 them, that the humic acid existing in a soil, sup- 

 posing all its carbon to be taken up and assiu ' 

 ted, will supply but a very small jjortion of that 

 which exists in the crop grown upon the soil 



The same remarks are applied to a crop of 

 wheat. From the known properties of metallic 

 oxides existing in wheat straw (the sulphates and 

 chlorides also contained in the ashes of wheat 

 straw not included,) it would be found, that the 



and 



wheat growing on 40,000 sipiare feet Hes 

 land would average J780 lbs. Hessian of straw, in- 

 dependently of the roots and grain, and the com- 

 position of this straw is the same as that of woody 

 fibre. Now, according to well-ascertained prop- 

 erties, it could receive hut 57 1-2 lbs. of humic 

 acid, which wonid supply with carbou only 85 

 lbs. Hessian of straw. 



Another calculaliim respects the amount of hu 

 mic acid which plants can receive through the 

 agency of rain water. The amount of rain fall- 

 ing in one of the most fertile districts of Ger- 

 many, during the months of April, May, June, 

 and July, is estimated to b'! 17 1-2 lbs. Hessian 

 upon every square foot of surface, or upon 40,- 

 000 square feel Hessian, 700,000 lbs. Hessian of 

 rain water. Now this extent of laud averages a 

 product of 28.')0 lbs. Hessian of corn (wheat) ; 

 3D0 lbs. of humic acid calculated to be absorbed 

 in this case, cannot account for the quantity of 

 carbon contained in the roots and leaves alone, 

 even if we siqipose the whole of the rain water 

 to be absorbed by the plants, whereas a large 

 portion of it must necessarily be lost or pass off 

 in some other form than through the orgau.s of 

 the plants. If these oalculaiions be correct, it is 

 evident that a small portion only of the carbou 

 existing in plants can be derived from the hu- 

 mus of t!ie soil. Another idea is suggested, viz. : 

 that as humus results from the decay of plants, 

 none existed at the time of the creation to form 

 the pabulum of the primitive vegetation. This 

 must have had other .sources of supply. Dr. Da- 

 na is of opinion that geine or humus is an origi- 

 nal creation, coeval with the creation of hydrogen 

 and oxygen and carbon. The conjecture is suffi- 

 ciently |)lausible, but it would be idle to advance 

 any opinion on thesuhject. The only (act which 

 can be said to favor one o|)inion above the other 

 is, that the plarits found in the earliest coal form- 

 ation are plants with small roots and expanded 

 foliage, implying that they drew their chief nour- 

 ishment frora the air. 



Ti;e inquiry which next arises is, if plants do 

 not derive their carbon, or but a very small por- 

 tion of it from the soil, whence is it obtained? 

 This intoreslins question I/iebig discusses at 

 large, and certainly with much ability. The^eed 

 itself contains thefirst supply of noiu-ishment for 



d froin the soil by the roots of plants, j-the roots of the infant germ of the plant. Before 



- ...I !....:„.-■. .. it appears above the surface, the humus in the 



soil quickens and invigorates its growth by Ihp 



upply of carbonic acid. This snp|)ly of car- 

 bonic acid is furnished by the accession of atmos- 

 pheric air from the loosening of the soil, the car- 

 bou of the humus combining with the oxygen of 

 the air to produce nourishment for the young 

 plant. When it rises above the surface, and its 

 external organs of nutrition, its stem and its 

 leaves, are fully developed, it ceases to draw 

 nourishment from the earth, and obtains all its 

 carbon from the air. It is not a new doctrine 

 that plants absorb carbonic acid from the atmo- 

 sphere. This fact has been long established; 

 but it is new that this is the principal source ; 

 and the inquiry naturally arises whether the at- 

 mosphere, containing, as it does, only a thou- 

 sandth part of carbonic acid, can furnish in this 

 way a supply of all the carbon which i^ required 

 by the plant. To this inquiry Liebig replies as 

 before, by making it matter of exact calculation. 



"It can be shown, that the atmosphere con- 

 tains 3,000 billion Hessian lbs. of carbon ; a quan- 

 tity which amounts to more than the weight of 

 all the plants, and of all the strata of mineral and 

 brown coal, which exist upon the earth. This 

 carbon is therefore more than adequate to all the 

 purposes for which it is required." — p. 74. 



The absorption of carbonic acid from the air, 

 in his opinion, is a purely chemical process. — 

 Many others have chosen to regard it as a vital 

 operation ; and have considered the leaves as re- 

 spiratory organs, resembling the lungs of ani- 

 mals. He does not admit the analogy, and thinks 

 that the cause of science is injured by the suppo- 

 sition of a resemblance, where no similitude ex- 

 ists. The absorption of carbonic acid from the 

 air, the assimilation of its carbon, and the return 

 of its oxygen to the air, are chemical processes, 

 effected "under the operation of light and heat. — 

 Without the aid of chemistry, they are inexplica- 

 ble ; with it, they become perfeclly intelligible. 

 The vital action creates nothing. It does not pro- 

 duce carbon, oxygen, or hydrogen ; but it puts 

 them into activity; and they then arrange them- 

 selves according to chemical principles; each or- 

 gan of the plant having ita own specific influence 

 in the production of the results. 



The author discusses, at large, the nature and 

 action of humus. Humus is merely decayed 

 vegetable substance, whose decay or destruction 

 is effected by the absorption of oxygen from the 

 air. Exclude it from the external air, and the (\j- 

 cay would cease; but would be renewed again as 

 it should be brought in contact with the oxygen 

 of the air. Woody fibre, in a state of decay, con- 

 sists of carbon and the elements of water. Alka- 

 line substances assist its decay. Humus, howev- 

 er, is not composed exclusively of woody fibre; 

 other substances are asssociated with it. We have 

 not the room to follow Liebig in his curious and 

 profound remarks on this subject, and can give 

 only a summary of his views. The constant ten- 

 dency of humus is to form carbonic arid by the 

 abstn'Ction of oxygsn from the air. The stirring 

 of the soil, and opening it to the effects of light 

 and heat and moisture, assist this process, by 

 bringing it in contact with the decaying humus. 

 It forms around itself an atmosfihere of carbonic 

 acid, and supplies carbonic acid to the plant in 

 Ihe first period of its growth. The roots of the 

 plants, in the beginning and before the formation 

 perform the functions of the leaves. They ex- 

 tract fi-om the soil the carbonic acid generated by 

 the humus. When a plant is matured, and when 

 the organs by which it receives its food from the 

 air, are perfected, the carbonic acid of the soil is 

 no further required. Humus does not afford 

 nourishment to plants, by being taken up into 

 their vessels in an unaltered state ; but only by 

 the supply of carbonic acid, which it generates 

 from the presence of atmospheric air. 



Hydrogen is another constituent of plants; for 

 woody fibre is composed of carbon and the ele- 

 ments of water. Water is decomposed under 

 the power possessed by plants of separating it.-* 

 elements, and of assimilating its hydrogen, and 

 dispensing with that portion of its oxygen not re- 

 quired by the plant in other processes of its 

 growth. Nitrogen is another constituent, found 

 in all plants ; abounding in some, and supposed 

 to form tho principal portion of the nutritive 

 properties of some of the cereal grains. The ni- 

 trogen of the air cannot enter into combination 

 with any element excepting oxygen. Tho com- 

 bination of nitrogen with hydrogen, in the pro- 

 portion of one volume of nitrogen and three of 



