AND HORTICULTURAL REGISTER. 



9 



PUIJLISHED BY JOSEPH BRECK & CO.. NO. 52 NORTH MA RKEt' STREET, (Ao«.cu.TuaA. Wah.hou...)-ALLEN PUTNAM, EDITOR. 



vol,. XIX.] 



BOSTON, WEDNESDAY EVENING, JUNE 9, 1841. 



[NO. 49. 



N. E. FARMER, 



From Liebig'g Organic Cliemislrjr. 



ON THE ORIGIN AND ACTION OP HUMUS. 



All plants and vegetable structures undergo two 

 processes of decomposition after death. One of 

 these is named fermenfation, the other decay, putre- 

 faction, or eremacausis* 



(Eremacaiisis is the art of gradual combination 

 of the combustible elements of a body with the oxy- 

 gen of the air; a slow combustion or oxidation 



The conversion of wood into humus, the formation 

 of acetic acid out of alcohol, nitrification, and nu- 

 merous other processes, are of this nature. Vege- 

 table juices of every kind, parts of animal and vege- 

 table substances, moist sawdust, blood, &c., cannot 

 be exposed to the air, without suffering immediate- 

 ly a progressive change of color and properties, 

 during which oxygen is absorbed. The property 

 of suffering this change is possessed in the highest 

 degree by substances which contain nitrogen.) 



Decay is a slow process of combustion, a pro- 

 cess, therefore, in which the combustible parts of a 

 plant unite with the oxygen of the atmosphere. 



The decay of woody fibre (the principal constitu- 

 ent of all plants,) is accompanied by a phenomenon 

 of a peculiar kind. This substance, in contact 

 with air or oxygen gas, converts the latter into an 

 equal volume of carbonic acid, and its decay ceases 

 upon the disappearance of the oxygen. If the car- 

 bonic acid is removed, and oxygen replaced, its de- 

 cay recommences, that is, it again converts oxyo-en 

 into carbonic acid. Woody fibre consists of car- 

 l)orj and the elements of water; and if we judce 

 jnly from the products formed during its decompo- 

 sition, and from those formed by pure i:harcoal 

 Jurned at a high temperature, we might conclude 

 hat the causes were the same in both : the decay 

 )f woody fibre-proceeds, therefore, as if no hydro- 

 fen or oxygen entered into its composition. 



A very long time is required for the completion 

 )f this process of combustion, and the presence of 

 vator is necessary for its maintenance : alkalies 

 iroinole it, but acids retard it; all antiseptic sub- 

 tances, such as sulphurous acid, the mercurial 

 alts, empyreumatic oils, &c., cause its complete 

 essation. 



Woody fibre. In a state of decay, is the siibstante 

 ailed humus. 



The conversion of woody fibre into the substan- 

 es termed humus and mould is, on account of its 

 ifluence on vegetation, one of the most remarka- 

 le processes of decomposition which occur in na- 

 ire. 



Decay is net less important in another point of 

 iew ; for, by means of its influence on dead vegc- 

 ible matter, the oxygen which plants retained 

 uring life, is again restored lo the atmosphere. 



The decomposition of woody fibre is etTected in 



three forms, the results of which are different, so the roots and by the organs above ground and ad- 

 that it is necessary to consider each separately. | .. ■- ' 



The first lakes place when it is in the moist 



'I he wi.rd eremacausis was proposed by ihe author 

 niP lime sincu, in order to e-tplain the Irue nature of 



itrelaction : it is compounded from two Greek words 



jniljiog slow combustion. — Tr. 



condition, and subject to free, uninterrupted access 

 of air; the second occurs when air is excluded ; 

 and the third when the wood is covered with wa- 

 ter, and in contact with putrefying organic matter. 

 It is known that woody fibre may be kept under 

 water or in dry air, for thousands of years without 

 suffering any appreciable change ; but that when 

 brought into contact with air in the moist condi- 

 tion, it converts the oxygen surroundini; it into the 

 same volume of carbonic acid, and is itself gradu- 

 ally changed into ii yrllowish brown, or black mat- 

 ter, of a loose texture. 



According to the experiments of De Saussure, 

 240 parts of dry sawdust of oak wood convert 10 

 cubic inches of oxygen into the same quantity of 

 carbonic acid, which contains 3 parts, by weight, 

 of carbon; while the weight of the sawdust is di- 

 minished by 1,5 parts. Hence 12 parts by weight, 

 of water, are at the same time separated from the 

 elements of the wood, 



It has already been mentioned, that pure woody 

 fibre contains carbon and the elements of water. 

 Humus, however, is not produced by the decay of 

 pure woody fibre, but by that of wood which con- 

 tains foreign soluble and insoluble organic substan- 

 ces, besides its essential constituent. 



Humus acts in the same manner in a soil per- 

 meable to air as in the air itself: it ia a continued 

 source of carbonic acid, which it emits very slowly. 

 An atmosphere of carbonic acid, formed at the ex- 

 pense of the oxygen of the air, surrounds every par- 

 ticle of decaying liiiinus. The cultivation of land, 

 by tilling and loosening the soil, causes a free and 

 unobstructed access of air. An atmosphere of car- 

 bonic acid is, therefore, "contained in every fertile 

 soil, and is the first and most important food for the 

 young plants which grow in it. 



In spring, when those organs of plants are ab- 

 sent, which nature has appointed for the assump- 

 tion of nourishment from the atmosphere, the com- 

 ponent substance of thi! seeds is exclusively em- 

 ployed in the formation of the roots. Each new 

 radicle fibril which a plant acquires, may be regard- 

 ed as constituting at the same time a mouth, a Fung, 

 ^r)d a stomach. The roots perform the functions 

 of the leaves from the first moment of their forma- 

 tion ; they extract from the soil their proper nutri- 

 ment, namely, the carbonic acid generated by the 

 humus. 



By loosening the soil which surrounds young 

 plants, we favor the access of air, and the formation 

 of carbonic acid ; and on the other hand the quan- 

 tity of their food is diminished by every difficulty 

 which opposes the renewal of air. A plant 

 itself effects this change of air at a certain period 

 of its growth. The carbonic acid, which protects 

 the undecayed humus from further change, is ab- 

 sorbed and taken away by the fine fibres of the 

 roots, and by the roots themselves ; this is replaced 

 by atmospheric air, by which process the decay is 

 renewed, and a fresh portion ol carbonic acid form- 



vances rapidly to maturity. 



When a plant is quite matured, and when the 

 organs by which it obtains food from the atmos- 

 phere, are formed, the carbonic acid of the soil ig 

 no further required. 



Deficiency of moisture in the soil, or its com- 

 plete dryness, does not now check the growth of a 

 plant, provided it receives from the dew and the 

 atmosphere as much as is requisite for the process 

 of assimilation. During the heat of summer it de- 

 rive.< its carbon exclusively from the atmosphere. 

 We do not know what height and strength na- 

 ture has allotted to plants ; we are acquainted only 

 with the size which tlicy usually attain. Oaks are 

 shown both in London andi Amsterdam, as remarka- 

 ble curiosities, which have- been reared by Chinese 

 gardeners, and are only one foot and a half in 

 height, although (heir trunks, barks, leaves, branch- 

 es, and whole liabitqs, evince a venerable age. 

 The. small turnip, grown at Teltow,* when placed 

 in a soil which yields as much nourishment as it 

 i;an take up, increases to several pounds in weitrht 

 The size of a plant is proportional to the surface 

 of Ihe organs which are destined to convey food to it. 

 A plant gains another mouth and stomach with eve- 

 ry new fibre of root and every new leaf. 



The power which roots possess of taking up 

 nourishment, does not cease as long as nutriment 

 is present. When the food of a plant is in greater 

 quantity than its organs require for their own per- 

 fect development, the superfluous nutriment is not 

 returned to the soil, but is employed in the forma- 

 tion of new organs. At the side of a cell already- 

 formed, another cell arises ; at the side of a twin- 

 and leaf, a new twig and leaf are developed. These 

 new parts could not have been formed had there 

 not been an excess of nourishment. The sugar 

 and mucilage produced in the seeds, form the nu- 

 triment of the young plants, and disappear during 

 the development of the buds, green sprouts, and 

 leaves. 



The power of absorbing' nutriment from the at- 

 mosphere, with which the leaves of plants are en- 

 dowed, being proportionate to the extent of their 

 surface, every increase in the size and number of 

 these parts is necessarily attended with an increase 

 of nutritive power, and a consequent further devel- 

 opment of new leaves and branches. Leaves, 

 twigs, and branches, when completely matured, aa 

 they do not become larger, do not need food for 

 their support. For their existence as organs, they 

 require only the means necessary for the perfor- 

 mance of the special functions to which they are 

 destined by nature ; they do not exist on their own 

 account. 



We know that the functions of the leaves and 

 other parts of plants are to absorb carbonic acid, 

 and with the aid of light and moisture, to appro- 

 priate its carbon. These processes are continually 

 in operation : they commence with the first forma- 



ed. 



"Teltow is a village near Berlin, where small lurnipa 

 are cultivated in n sandy soil: ihey are much esteemed, 

 A plant at this time receives its food both by I and weigh rarely above one ounce. 



