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RIAU ESET in 20 tay: ites a Beads de fe ee See. : aah ee THe Phin i SH ita i ay ee oes ae Se Se eee q3gites rinig att aE Re eee ste) Pisa, ested i RPO dad HIME TA 4 Pat bate DWE ore sad te if Hd: Se URE Dia ite ty i aan a AY 3 year at t } ray hat . { : Stet thy bt Ve BES Ras rae pee Uy e4s bee S HD an et catty eg ae buns AY Lara) ieee ryt 3 Haar bts Aig Hate Ad } ' E Hie ¥ Teas te hes Paes 4 : ikl sdy Ma 4 pes} Tk ek ae fad, Aas ee Soles eae S SATO ee VS Airey regi tet fat ie Ut ey 1s) 7 DAB AIA 4 4 [PS pra WAU ENR a é t r ‘ ; t 4 os yt ’ 4 Heh aa 47% ‘ rie 2 Ht tte pte F i » s e saty « : | , ‘ > egy or é ‘ ¥ , mat} 5 4 ate p int) 4 seas ihsé , 4 . ‘ i j ’ ‘ , { me hes i ils Fy ua is q Pie i % ; } zt rea" : 4 ‘ ¥ Hf 9, 4 t: tif) ' fer by ‘ f } y { Deut ; fat see 44 j - 4 : a hg * 2 at eH ae ae bet Wah: | ~ \ HOW CROPS FEED. LN EN A TREATISE ON THE ATMOSPHERE AND THE SOIL AS RELATED TO THE Nutrition of Agriculturai Plants. WITH ILLUSTRATIONS. BY SAMUEL W. JOHNSON, M.A. PROFESSOR OF ANALYTICAL AND AGRICULTURAL CHEMISTRY IN THE SHEFFIELD SCIENTIFIC SCHOOL OF YALE COLLEGE; CHEMIST TO THE CONNEC- TICUT STATE AGRICULTURAL ,SOCIETY; MEMBER OF THE NATIONAL ACADEAY ,C#, SCIENCES. >» 2 >, \ NEW YORK: ORANGE JUDD AND COMPANY, 245 BROADWAY. - J a, Ae In the Clerk’s Office of the District Dowt of tae United States for District of New York, ata . , § ws ~ s gh v on ‘ \ ’ as o. \ ¥ ; 4 aa ‘ Gast : : ‘3 ET ee ak CASA ie Fae | ry! pry ts : aa § y ? Pe Rey % - \ " Ss ete f ee a . eH ‘ 3 f a + ue »- J LAR ae o> PREFACE. The work entitled “ How Crops Grow” has been re- ceived with favor beyond its merits, not only in America, but in Europe. It has been republished in England under the joint Editorship of Professors Church and Dyer, of the Royal Agricultural College, at Cirencester, and a translation into German is soon to appear, at the instiga- tion of Professor von Liebig. The Author, therefore, puts forth this volume—the com- panion and complement to the former—with the hope that it also will be welcomed by those who appreciate the sci- entific aspects of Agriculture, and are persuaded that a true Theory is the surest guide to a successful Practice. The writer does not flatter himself that he has produced a popular book. He has not sought to excite the imagi- nation with high-wrought pictures of overflowing fertility as the immediate result of scientific discussion or experi- ment, nor has he attempted to make a show of revolution- izing his subject by bold or striking speculations. His office has been to digest the cumbrous mass of evidence, in which the truths of Vegetable Nutrition lie buried out 5 ‘ VI PREFACE, of the reach of the ordinary inquirer, and to set them forth in proper order and in plain dress for their legiti- mate and sober uses. It has cost the Investigator severe study and labor to — discover the laws and many of the facts which are laid down in the following pages. It has cost the Author no little work to collect and arrange the facts, and develop their mutual bearings, and the Reader must pay a similar price if he would apprehend them in their true signifi- cance. In this, as in the preceding volume, the Author’s method has been.to bring forth all accessible facts, to present their evidence on the topics under discussion, and dispassion- ately to record their verdict. If this procedure be some- times tedious, it is always safe, and there is no other mode of treating a subject which can satisfy the earnest inquirer. It is, then, to the Students of Agriculture, whether on the Farm or in the School, that the Author commends his book, in confidence of receiving full sympathy for its spirit, whatever may be the defects in its execution, CONTENTS. RBS ERISETCTRCIN «0 oh alta te sini dao cu ac wna Osaka oeeial (a ea'n's Gioia woplele walsh oa-aelse see 20aSisejak'é DIVISION I. THE ATMOSPHERE AS RELATED TO VEGETATION. CHAPTER: I. ATMOSPHERIC AIR AS THE Foop oF PLANTS. os. cnemical Composition of the Atmosphere... 0.2.06 cle. ces eta ete aats 21 § 2. Relation of Oxygen Gas to Vegetable Nutrition....................2032..22 § 3 “Nitrogen Gasto ‘°° Ber es oe PRN Meas fairs) Se Atcha wisiavaib oa is 26 § 4 oy ** Atmospheric Water to Vegetable Nutrition.................. 34 § 5 Re ““ Carbonic Acid Gas “ 8 eS Sent AAP ESS BE tae eee 38 § 6 ‘ ** Atmospheric Ammonia to ‘“ i EE aeRO nS. OAR ee 49 Tig (OAS a Bs eG Ee ee ie tani te he ie ar Ate ARR oe ee nN 63 § 8. Compounds of Nitrogen and Oxygen in the Atmosphere................. 70 ee wer teeredients of the Atmosphere: . .........s0.+- 5-2 o561 0 ceo sesinonen 91 § 10. Recapitulation of the Atmospheric Supplies of Food to Crops........... 94 ole seimlation of Atmospheric Food)... 2.24.6 s208 eae sseics s «oie ss se tis alk OK § 12. Tabular View of the Relations of the Atmospheric Ingredients to the [oe ROLL ici balm ler gy eo Ran Soi AR a 2 AB 98 CHAPTER II. THE ATMOSPHERE AS PHYSICALLY RELATED TO VEGETATION. § 1. Manner of Absorption of Gaseous Food by Plants..........0..2eeeeee eee 99 DIVISION II. THE SOIL AS RELATED TO VEGETABLE PRODUCTION. CHA PLE RI. I STMLR ME Stereo Sac abs ve acc gua acasacWece wneeesvesteosine «6 ow kOe 7 VIII HOW CROPS FEED. CHAP TE Eat. Ondim Any WormMAtTiIon oF SOUS. o 1.6: cc.2cucess vaave see 9a teen 106 § 1. Chemical Hlements/Of TROCKS. 0.2.05 joe c nes oe cee nce ee ta eae ee ene 107 § 2. Mineralogical Mlements of Rocks) 7... ..52 25. iiciccise ns cee stele pee 108 § 8. Rocks, their Kinds and Characters. : ... . 2.2.5. 20i...52.000h) sos 117 § 4. -Conversion of Rocks into Soll ..:5.....-.....cus20.00+--2a (ocean 122 § 5. Incorporation of Organic Matter with the Soil, and its Effects........... 185 gi. § 2. PHY ga. § 2. § 3. § 4, § 5. § 6. § 7. § 8. § 9. THE § 1. § 2. g 3. § 4. § 5. § 6. § 1. § 8. § 9, CHAPTER 221i; Kinps oF Sorts, THEIR DEFINITION AND CLASSIFICATION. Distinctions of Soils based upon the Mode of their Formation or Deposi- TOD i, oiesicciv ect Sa aierreleens & os aati iate os cle ate 5a wea o\ die tepealate le ake e eee 142 Distinctions of Soils based upon Obvious or External Characters........ 146 CHAPTER IV. SICAL .CHARACTERS OF THE SOUL;.... 4.2 .\s 00) asa on picicvesie sls sapien 157 Wieieht Of SOUS y o.55 06... 5egce.e bese ns tales cle eusiagl cuctwievetee ed ee lore ole nicte ate aa 158 stave Of DEVISION s5.0'.5 2 )oS cco cio wa o1s'n:he oo Ve clelent a's x 94 Unie eee ern 159 Absorption of ‘Vapor of Water... 2... 00 i dcee sense segs vse senee se 161 Condensation Of ‘Gases... 5... secs set ee se shee tile! sine nate ee 165 Power of Removing Solid Matters from Solution.................-.+-. «+ 171 Permeability to Liquid Water. Imbibition. Capillary Power........... 1%6 Changes of Bulk by Drying and Frost.............ccceeceeceeccees socee 183 WA GHESTVENESB 2.5 Fs bode Holic ck rials ole wtee sicieibie te cie'ne ame ieee Us Cette eee 184 Melations to Hed, . «5 woes pec. cce econ nes aielese c/o pep Gib oteie cisiefele etait eamamman 186 CHAPTER YV. Som, As A SouRCE oF Foop To Crops: INGREDIENTS WHOSE ELEMENTS ARE OF ATMOSPHERIC ORIGIN. The Free Water of the Soil in its Relations to Vegetable Nutrition...... 199 The Air of the Soil. eos ess ae cistera elon bss cleia wie reece eae “eee Non-nitrogenous Organic Matters. Humus..............cecesencccee ween 222 The Ammonia‘of the Soils co. ye wees es amine emieln » » ale leleisls stoie.clen oe ee 238 Nitric Acid (Nitrates) of the Soil). 5 2... fe2 coon 02 Ss ce ve cee 251 Nitrogenous Organic Matters of the Soil. Available Nitrogen........... 274 Decay. of Organic Matters... . 20 cei 5 cat ece as cle vicyn'e isloln eiciais a lalstm eetenanee 289 Nitrogenous Principles of Urine... .....-.5.- 0s 04004s+00es) see 293 Comparative Nutritive Value of Ammonia-Salts and Nitrates............ 300 CONTENTS. : IX CHAP T Ext .V-1. Tuer Som AS A SOURCE OF Foop To Crops: INGREDIENTS WHOSE ELEMENTS ARE DERIVED FROM ROCKs. § 1. General View of the Constitution of the Soil as Related to Vegetable apie Bae Re eee ee ere BAG cishct ated AMG 6 oS aisle abi te the wate 3805 SOT OULLION OF TE SOU. so. 25 occ’ candies wees ods acceusecddeadcdceses 309 See oation Of the Soilin Strong Acids. .... 2.25 .cccceesececeacuses, deacecce 329 Seeerortion of Soil Insoluble-int Acids... 0.5.6.2 ceca obec eee ceweseeencaaas 330 § 5. Reactions by which the Solubility of the Elements of the Soil 1s al- tered. Solvent Effects of Various Substances. Absorptive and PNG OE ONL: OF SOUS, ic os tw aks Bice ae ee eid Sede cee eis oe se alaeice viels'e 381 BRUIT AUG CORCINGION, 5% s:0'a0,cs'scaseasiansces vevevave viene onede sans cesoe00L 1 Ay me aah Satie INDEX. Absorption and displacement, law Tl, .Ad dee oeio merce 336 Absorptive power of soils......... 333 a s * cause of.348, 354 cs = ‘* sjonificance Oleri te, atajsia 374 BMGT Site SOM cara cln'c aicie eislesie= >i ole serve 223 Pa AbROLDE. DY: SOUS: :. 4 i). 0-620 305 DAEMON Ses ie Se Ree cae 165 Adhesiveness of soils.............. 184 Air, atmospheric, composition of.. 21 ‘‘ within the plant, composition Ds GARD aa peer Pens ere 45 Alkali-salts, solvent effect of....... 130 PMMGUNGDISMN: £olc ecco aces fod tee ean 66 PPMITCRVITINER ais cielo etic wless cove ascieisisiesies 145 Aluminum, alumina.............--- 107 PASTE gorc'a vso.0:6 = siwiefoleis, 0.00.0 so oie esis 276 Amide-like bodies. Morrell aiskesataerete 277, 300 PRRRIR TIO TI Soe een cisics bvw'sis) ' Sere? sidie.e 49, 54 sf absorbed by clay... .248, 267 = * Wer OAs os cce/ sake 360 oe es * plants....56, 98 % condensed in soils ...... 240 bes conversion of into nitric MCL cltera eieyeieicl oo aeee = 85 is evolved from flesh decay- ing under charcoal..... 169 . fixed by gypsum......... 244 Os In» atmosphere. -....2...5- 54 a so ‘© how formed.77, 85 “ OL TAM CUCa... «cies see aie 60 * of the soil, formation of.289 a + $6 chemically combined.243 Sy $e physically condensed.240 ro a “ quantity of. .248 = Fy ‘solubility of .246 volatility of. .244 Ammonia-salts and nitrates, nutri- LIVEN VALUE Ole itear sn ais oieirte Navaleie poe 289 DCI MESCENCE 2, acie,s's one ca sates 168 BRERELUS st sec ost 3 ecoisietic tes nine wiseista 197 MIRC RV etteatiaisee ciclo pars calc oso eens 189, 195 Mision OF BASES... owe 3 seen 100 LD Cyr ert lee ce eae Rate SEES SINE . 120 ROR CMa: Seine octal Sereerae elt col OO PMOMEILG 2 = 22 S05 os stie'eis.c vavsicers ab Os Ras (al BEARER 3m vie oieiat oSewe ac ancien yotee loo Drain water, composition of....... 312 NAR ee eane ro erts ote shee eis coos vie Ee Se en os 144 Dye stuns, sxe Of. 32.2555 ls. ee 174 Rabb Ghos@tie. cic. 6 cece wae aac. tie 171 IPCPAACAUBIS Se a. ac seem cine ae eatie 289 Evaporation, produces cold........ 188 ee amount of, from soil.197 HMQIATLOB fs. ose peace eet s 202, 206 Hxposure Of. SOll so. .2, csscccee ene vee 195 HELA mee. tae tenia: wee cconeien s 108 ‘+’ growth of barley in.... .. 160 Hermentation ./..\0..)..0... 4. ae see 290 Fixtation of bases in the soil...... 339 Frost, effects of, on rocks..... .... 124 ig oy ‘OR ROMS "242 os 184, 185 PORUIPIRE SUED. 9 55's Saetts aco cietbinte he me mee 258 GAREE, absorbed by the plant Seana 103 * ** porous bodies. .167 + “f ete (07 0| Pe 165, 166 st GiasiOn Of... siccbes see ea 100 td OSINOSC 400.7: J heweceic ano 102 RMR S Foie Us 3 y's vie foe bie hss tee 124 HOW CROPS FEED. GIy ING... oi. ois scien cca eo 296 Glycocoll .. .+../0::5<+s:t ses aa 296° Gnelss.........t2s9s02 ae eee 119 Granite. «2... isi sera 118, 120 Gravely... > sss 5<=s06 deen 152 * swarmth Of. 355.4 Gls 195 GUANIN . .2:.0:. 0s acensie> ov cet ee 296 GYPSUM 23 a5. cw cnjen eh 115 we does not directly absorb Water... 200.08. -162 «¢ ' 4ixes ammonia... 25002 eee 244 Mardpan «.....\., 0006+ 0006 sate 156 Heat, absorption and radiation of.. 188, 193 «developed in flowering....... 24 ‘¢ \ Of Soils. ./<. 4 187 Hippuric acid. “3... cseases sane 295, 277 Hornblende. ..: 33/052. cose eee 112 Hydration of minerals............. 127 Hydraulic cement....... \e'ss ail eee Hydrochloric acid gas.............. 93 Hydrogen, supply of, to plants..... 95 SF im: decay: : 32 Secs 291 Hydrous silicates, formation of... .352 Hygroscopic quality................ 164 Humates.. 5:25 1 svslos ene eee 230 Humic acid. \......0ss. see 226, 229 Hum 30k Sa 236, 229 AMM 5256. st chee eee 186, 224, 276 ‘¢ absorbent power for water. .162 ‘* absorbs salts from solutions.172 ‘* action on minerals.......... 138 “* .- chemical nature’of.2. 222.00 188 ** does it feed the plant?...... 2382 ‘* not essential to crops........ 238 46S Va "OLoe veer seseien eee 182 Todine in sea-water............-- 322 Isomorphism ;.2'...i.sase sess eee 111 Kreatin.:. .':5'. 5.4) mses abate eee ene 196 Kaolinite.-..':iseudes tare 113, 132 Latent ‘heat: 4.0.0. toe ee eee 188 Lawes’ and Gilbert’s wheat experi- ments.......:3 , + co daiaapeeeeee 372 Leucite +52... dees peeve doe eee 113 Lime; effects: of:.\¢...-.eneeceee 184, 185 Limestone: 2's 3 i523. 23 tele 121, 122 TOaM ss ch 55s ice | ee 154 Suysimeter,.. 2.2. .< cs csaeeee eee 314 Maonesites*. 6. s\cisiss2% sigeeeeeeneee 115 Marble: s. ois Js. 06s. since 121 Marl, 22 c2c hid. ioe bec eee 155 Marslt 288). 00)... 00 =. ca 91, 99 LV (Coe: RO ep AR 109 INDEX. ROMER PATE Soc e accs of a teacess «= 119 “DST SS ee 106, 108 ee MyeraitOn: Of. 3. 222i. st, aoe a 203 Wool, hygroscopic, )..25.2.seee een 164 Zeolites.......- oa cio ale tte aa eee - HOW CROPS FEED. HOW CROPS FEED. INTRODUCTION, In his treatise entitled “ How Crops Grow,” the author has described in detail the Chemical Composition of Agri- cultural Plants, and has stated what substances are indis- pensable to their growth. In the same book is given an account of the apparatus and processes by which the plant takes up its food. The sources of the food of crops are, however, noticed there in but the briefest manner. The present work is exclusively occupied with the important and extended subject of Vegetable Nutrition, and is thus the complement of the first-mentioned treatise. Whatever information may be needed as preliminary to an under- standing of this book, the reader may find in “ How Crops Grow.” * That crops grow by gathering and assimilating food is a conception with which all are familiar, but it is only by following the subject into its details that we can gain hints that shall apply usefully in Agricultural Practice. * It has been at least the author’s aim to make the first of this series of books prepare the way for the second, as both the first and the second are written to make possible an intelligible account of the mode of action of Tillage and of Fertilizers, which will be the subject of a third work. Ly 18 HOW CROPS FEED. When a seed germinates in a medium that is totally destitute of one or all the essential elements of the plant, the embryo attains a certain development from the mate- rials of the,seed itself (cotyledons or endosperm,) but shortly after these are consumed, the plantlet ceases to in- crease in dry weight,* and dies, or only grows at its own expense. A similar seed deposited in ordinary soil, watered with rain or spring water and freely exposed to the atmosphere, evolves a seedling which survives the exhaustion of the cotyledons, and continues without cessation to grow, forming cellulose, oil, starch, and albumin, increases many times—a hundred or two hundred fold—in weight, runs normally through all the stages of vegetation, blossoms, and yields a dozen or a hundred new seeds, each as perfect as the original. It is thus obvious that Air, Water, and Soil, are capa- ble of feeding plants, and, under purely natural conditions, do exclusively nourish all vegetation. In the soil, atmosphere, and water, can be found no trace of the peculiar organic principles of plants. We look there in vain for cellulose, starch, dextrin, oil, or al- bumin. The natural sources of the food of crops consist of various salts and gases which contain the ultimate ele- ments of vegetation, but which require to be collected and worked over by the plant. The embryo of the germinating seed, like the bud of a tree when aroused by the spring warmth from a dormant state, or like the sprout of a potato tuber, enlarges at the expense of previously organized matters, supplied to it by the contiguous parts. As soon as the plantlet is weaned from the stores of the * Since vegetable matter may contain a variable amount of water, either that which belongs to the sap of the fresh plant, or that which is hygroscopically re- 1ained in the pores, all comparisons must be made on the dry, i. é., eet substance. See *‘ How Crops Grow,” pp. 53-5. INTRODUCTION. 19 mother seed, the materials, as well as the mode of its nu- trition, are for the most part completely changed. Hence- forth the tissues of the plant and the cell-contents must be principally, and may be entirely, built up from purely inorganic or mineral matters. Jn studying the nutrition of the plant in those stages of its growth that are subsequent to the exhaustion of the cotyledons, it is needful to investigate separately the nu- tritive functions of the Atmosphere and of the Soil, for the important reason that the atmosphere is nearly con- stant in its composition, and is beyond the reach of human influence, while the soil is infinitely variable and may be exhausted to the verge of unproductiveness or raised to the extreme of fertility by the arts of the cultivator. In regard to the Atmosphere, we have to notice minutely the influence of each of its ingredients, including Water in the gaseous form, upon vegetable production. The evidence has been given in “ How Crops Grow,” which establishes what fixed earthy and saline matters are essential ingredients of plants. The Soil is plainly the exclusive source of all those elements of vegetation which cannot as- sume the gaseous condition, and which therefore cannot ex- ist in the atmosphere. The study of the soil involves a con- sideration of its origin and of its manner of formation. The productive soil commonly contains atmospheric elements, which are important to its fertility; the mode and extent of their incorporation with it are topics of extreme prac- tical importance. We have then to examine the signif- icance of its water, of its ammonia, and especially of its nitrates. These subjects have been recently submitted to extended investigations, and our treatise contains a large amount of information pertaining to them, which has never before appeared in any publication in the English tongue. Those characters of the soil that indirectly affect the growth of plants are of the utmost moment to the farm- er. It is through the soil that a supply of solar heat, with- 20 HOW CROPS FEED. out which no life is possible, is largely influenced. Water, whose excess or deficiency is as pernicious as its proper quantity is beneficial to crops, enters the plant almost exclusively through its roots, and hence those qualities of the soil which are most favorable to a due supply of this liquid demand careful attention. The absorbent pow- er of soils for the elements of fertilizers is a subject which is treated of with considerable fullness, as it deserves, Our book naturally falls into two divisions, the first of which is devoted to a discussion of the Relations of the Atmosphere to Vegetation, the second being a treatise on the Soil. ——— DIVISION LIL. THE ATMOSPHERE AS RELATED TO VEGETATION. GHiAPrT ER: -F¥, ATMOSPHERIC AIR AS THE FOOD OF PLANTS. mee CHEMICAL COMPOSITION OF THE ATMOSPHERE. A multitude of observations has demonstrated that from ninety-five to ninety-nine per cent of the entire mass (weight) of agricultural plants is derived directly or indi- rectly from the atmosphere. 3 The general composition of the Atmosphere is familiar to all. It is chiefly made up of the two elementary gases, Oxygen and Nitrogen, which have been described in “How Crops Grow,” pp. 33-39.* These two bodies are present in the atmosphere in very nearly, though not altogether, invariable proportions. Disregarding its other ingredients, the atmosphere contains in 100 parts By weight. By volume. CRIP EN ta) 0d ose ica roc ts | aie ee 20.95 ROSEN (osisi0 25 os, 2- Mean ges iio veo Wags wales a 79.05 100.00 100.00 Besides the above elements, several other substances oc- * In our frequent references to this book we shall employ the abbreviation H. C..G: 21 22 HOW CROPS FEED. cur or may occur in the air in minute and variable quanti-. ties, viz. : Water, as vapor...average pipes by weight, -]100 Carbonic acid eau a BS yeti 5110-000 Ammonia ue ty Ss 3: 1 Iso- 000+ ois ? Ozone ge 4 ee ‘¢ minute traces. Nitric acid 66 6c 6 yay a3 6c Nitrous acid ia9 «ec (<9 ce (73 ae Marsh gas “ce ac 74 79 ce its In air of ( C2tPonic oxide, Re ae eae 56 * Sulphurous acid, " eae x " towns. Sulphydric acid ss * a i eS Miller gives for the air of England the following aver- age proportions by volume of the four most abundant in- eredients. —(Llements of Chemistry, part IL., p. 30, 3d Ed. “a (boa ed oh BF PRES tents PPA ey oS fo sd 20.61 PUGET OOEIG «5,0 2 gms s/o cup alee eal ae 77.95 Carbone 2Gid, |... o6-sces$itise weenie 04 BV RICE-WAPOT, 08 osc. oases wie moet ate ee eee 1.40 100.00 We may now appropriately proceed to notice in order each of the ingredients of the atmosphere in reference to the question of vegetable nutrition. This is a subject re- garding which unaided observation can teach us little or nothing. The atmosphere is so intangible to the senses that, without some finer instruments of investigation, we should forever be in ignorance, even of the separate exist- ence of its two principal elements. Chemistry has, how- ever, set forth in a clear light many remarkable relations of the Atmosphere to the Plant, whose study forms one of the most instructive chapters of science. § aM RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION. Absorption of Oxygen Essential to Growth.—The ele- ment Oxygen is endowed with great chemical activity. This activity we find exhibited in the first act of vegeta- ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 3 tion, viz.: in germination. We know that the presence of oxygen is an indispensable requisite to the sprouting seed, and is possibly the means of provoking to action the dor- mant life of the germ. The ingenious experiments of Traube (H. C. G., p. 326.) demonstrate conclusively that free oxygen is an essential condition of the growth of the seedling plant, and must have access to the plumule, and especially to the parts that are in the act of elongation. De Saussure long ago showed that oxygen is needful to the development of the buds of maturer plants. He ex- perimented in the following manner: Several woody twigs (of willow, oak, apple, etc.) cut SS in spring-time just before the buds should unfold were placed under a bell-glass containing common air, as in fig. 1. Their cut extremities stood in water held in a small vessel, while the air of the bell was separated from the external atmosphere by the mercury contained in the large basin. Thus situated, the buds opened as in the free air, and oxygen gas was found to be consumed in considerable quan- Fig. 1. tity. When, however, the twigs were confined in an atmosphere of nitrogen or hydrogen, they decayed, with- out giving any signs of vegetation. (Zecherches sur la Vegetation, p. 115.) 7 The same acute investigator found that oxygen is ab- sorbed by the roots of plants. Fig. 2 shows the arrange- ment ‘by which he examined the effect of different gases on these organs. A young horse-chestnut plant, carefully lifted from the soil so as not to injure its roots, had the latter passed through the neck of a bell-glass, and the stem was then cemented air-tight into the opening. The bell 24 HOW CROPS FEED. was placed in a basin of mercury, ©, D, to shut off its con- tents from the external air. So much water was intro- duced as to reach the ends of the principal roots, and the space above was occupied by com- mon or some other kind of air. In one experiment carbonic acid, in a second nitrogen, in a third hydro- gen, and in three others common air, was employed. In the first the roots died in seven or eight days, in the second ang third they perish- ed in thirteen or fourteen days, while in the three others they re- mained healthy to the end of three weeks, when the experiments were concluded. (Recherches, p. 104.) Flowers require oxygen for their development. Aquatic plants send their flower-buds above the water to blossom. De Saussure found Fig. 2. that flowers consume, in 24 hours, several or many times their bulk of oxygen gas. This absorption proceeds most energetically in the pistils and stamens. Flowers of very rapid growth experience in this process, a considerable rise of temperature. Garreau, observing the spadix of Arum italicum, which absorbed 284 times its bulk of oxygen in one hour, found it 15° F. warmer than the surrounding air. In the ripening of fruits, oxygen is also absorbed in small quantity. The Function of Free Oxygen.—All those processes of growth to which free oxygen gas is a requisite appear to depend upon the transfer to the growing organ of mat- ters previously organized in some other part of the plant, and probably are not cases in which external inorganic. bodies are built up into ingredients of the vegetable struc- ture. Young seedlings, buds, flowers, and ripening fruits, ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 25 have no power to increase in mass at the expense of the atmosphere and soil; they have no provision for the ab- sorption of the nutritive elements that surround them ex- ternally, but grow at the expense of other parts of the plant (or seed) to which they belong. The function of free gaseous oxygen in vegetable nutrition, so far as can be judged from our existing knowledge, consists in effecting or aiding to effect the conversion of the materials which the leaves organize or which the roots absorb, into the proper tissues of the growing parts. Free oxygen is thus probably an agent of assimilation. Certain it is that the free oxygen which is absorbed-by the plant, or, at least, a corresponding quantity, is evolved again, either in the un- combined state or in union with carbon as carbonic acid. Exhalation of Oxygen from Foliage.—The relation of the leaves and green parts of plants to oxygen gas has thus far been purposely left unnoticed. These organs like- wise absorb oxygen, and require its presence in the atmos- phere, or, if aquatic, in the water which surrounds them; but they also, during their exposure to light, exhale oxygen. This interesting fact is illustrated by a simple experiment. Fill a glass funnel with any kind of fresh leaves, and place it, inverted, in a wide glass containing water, fig. 3, so that it shall be completely immersed, and displace all air from | its interior by agitation. Close the |= neck of the funnel air-tight by | a cork, and pour off a portion of the water from the outer vessel. Expose now the leaves to strong sunlight. Observe that very soon minute bubbles of air will gather on the leaves. These will gradually increase in size and detach themselves, and after an hour or two, enough gas will accumulate in the neck of the funnel to enable the experimenter to 2 26 HOW CROPS FEED. prove that it consists of oxygen. For this purpose bring the water outside the neck toa level with that inside; have ready a splinter of pine, the end of which is glow- ing hot, but not in flame, remove the cork, and insert the ignited stick into the gas. It will flame and burn much more brightly than in the external air. (See H. C. G., p. 35, Exp. 5.) To this phenomenon, one of the most im- portant connected with our subject, we shall recur under the head of carbonic acid, the compound which is the chief source of this exhaled oxygen. § 3. RELATIONS OF NITROGEN GAS TO VEGETABLE NUTRITION. Nitrogen Gas not a Food to the Plant.—Nitrogen in the free state appears to be indifferent to vegetation. Priestley, to whom we are much indebted for our knowl- edge of the atmosphere, was led to believe in 1779 that free nitrogen is absorbed by and feeds the plant. But this philosopher had no adequate means of investigating the subject. De Saussure, twenty years later, having command of better methods of analyzing gaseous mix- tures, concluded from his experiments that free nitrogen does not at all participate in vegetable nutrition. Boussingault’s Experiments,—The question rested un- til 1837, when Boussingault made some trials, which, how- ever, were not decisive.- In 1851-1855 this ingenious chemist resumed the study of the subject and conducted a large number of experiments with the greatest care, all of which lead to the conclusion that no appreciable amount of free nitrogen is assimilated by plants. His plan of experiment was simply to cause plants to grow in circumstances where, every other condition of de- velopment being supplied, the only source of nitrogen at ATMOSPHERIC AIR AS THE FOOD OF PLANTS. oF. their command, besides that contained in the seed itself, should be the free nitrogen of the atmosphere. . For this purpose he prepared a soil consisting of pumice-stone and the ashes of stable-manure, which was perfectly freed from all compounds of nitrogen by treatment with acids and in- tense heat. In nine of his earlier experiments the soil thus prepared was placed at the bottom of a large glass globe, B, fig. 4, of 15 to 20 gallons’ capacity. Seeds of cress, dwarf beans, or lupins, were deposited in the soil, and a proper supply of water, purified for the purpose, was add- ed. After germination of the seeds, a glass globe, D, of about one-tenth the capacity of the larger vessel, was filled with carbonic acid (to supply carbon), and was secured air- tight to the mouth of the latter, com- munication being had between them by the open neck at C. The apparatus was then disposed in a suitably lighted place in a garden, and left to itself for a period which va- ried in the different experiments from 13 to 5 months. At the conclusion of the trial the plants were ‘lifted out, and, to- gether with the soil from which their roots could not be entirely separated, were subjected to chemical analysis, to determine the amount of nitrogen which they had assimilated during growth. The details of these trials are contained in the subjoined 28 HOW CROPS FEED. \ Table. The weights are expressed in the gram and its fractions. mate (ule Sl : UraltON | 8) wZ sa} §s 1$8.| 478 S| Kind of Plant. of iSs/ Rs | SS | 88 [Sad tls S Experiment. 3H SS” SS SR ss" s oe = abe Ree ee fe SQ ch Dwarf bean. | 53.222. 2 months 1 | 0.780} 1.87 |0.0349 0.0340|—0.0009 2 CT SES Se ae eh 2 10 | 0.877 | 0.54 |0.00780.0067/—0.0011 S| PSORIT sh. a oeiek See wee es Hels 1 | 0.530} 0.89 |0.0210 0.0189;—0.0021 4 Be fs datoratavetate «5 Btery fet oe Biss 1 | 0.618 | 1.13 |0.0245)0.0226/—0.0019 Ol NOM Bee sak codec aetiee au 4 | 0.189 | 0.44 |0.0031)0.0030/—0.0001 6) Spine Sin eee 14% ‘* 2 | 0.825 | 1.82 |0.0480/0.0483|+-0.0003 q NEMS ihe che tar aor 2 s 6 | 2.202} 6.73 |0.1282)0.1246|—0.0036 8 Tt Sean ae roe 7 weeks 2 | 0.600} 1.95 |0.0349|0.0339|—0.0010 9 Si 5 IS ea Wee sae Gh, s 1 | 0.343} 1.05 |0.0200)0.0204|-+-0.0004 10 Peep 2 bie tig IR ec 6 if 2 | 0.686 | 1.53 |0.0399|0.0397;—0.0002 a1 wart bean. 7.2 i... 2 months 1 | 0.%92| 2.35 |0.0354/0.0360/-+-0.0006 12 a & pe ae Fee a 38 1 Bec 2.80 |0.0298)0.0277|—0.0021 ROSMS A Ce ciao vese silos ys 3 .008 18 4 em eet ntns Goes ioe 2. {as oe 10 0,036 ¢ 0.65 |0.0013/0.0013) 0.0000 TID es ee 2a) 2h 5 months 21) 0627 pe roy |_ 14/4 Us arate hae Sigcoer Ns ie eet 5.76 |0.1827/0.1697/—0.0130 14) hs eS fo Eee Saks Soke vceu Is tele 11.720 | 30.11 |0.6135|0.5868/—0.0247 While it must be admitted that the unavoidable errors of experiment are relatively large in working with such small quantities of material as Boussingault here employed, we cannot deny that the aggregate result of these trials is de- cisive against the assimilation of free nitrogen, since there was a loss of nitrogen in the 14 experiments, amounting to 4 per cent of the total contained in the seeds; while a gain was indicated in but 3 trials, and was but 0.13 per cent of the nitrogen concerned in them.—(Boussingault’s Agronomie, Chimie Agricole, et Physiologie, Tome I, pp- 1-64.) | The Opposite Conclusions of Ville.—In the years 1849, °50, °51, and *52, Georges Ville, at Grenelle, near Paris, experimented upon the question of the assimilability of free nitrogen. His method was similar to that first employed by Boussingault. The plants subjected to his trials were cress, lupins, colza, wheat, rye, maize, sun-flowers, and to- bacco. They were situated in a large octagonal cage made of iron sashes, set with glass-plates. The air was ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 29 constantly renewed, and carbonic acid was introduced in proper quantity. The experiments were conducted ona larger scale than those of Boussingault, and their result was uniformly the reverse. Ville indeed thought to have established that vegetation feeds on the free nitrogen of the air. To the conclusions to which Boussingault drew from the trials made in the manner already described, Ville objected that the limited amount of air contained in the glass globes was insufficient for the needs of vegetation ; that plants, in fact, could not attain a normal development under the conditions of Boussingault’s experiments.— - (Ville, Recherches sur la Vegetation, pp. 29-58, and 53-98.) Boussingault’s Later Experiments.—The latter there- upon instituted a new series of trials in 1854, in which he proved that the plants he had previously experimented upon attain their full development in a confined atmosphere under the circumstances of his first experiments, provided they are supplied with some assimilable compound of ni- trogen. He also conducted seven new experiments in an apparatus which allowed the air to be constantly renewed, and in every instance confirmed his former results.— (Agronomie, Chimie Agricole et Physiologie, Tome I, pp. 65-114.) The details of these experiments are given in the follow- ing Table. The weights are expressed in grams. > |S S [5 ES SS < Duration |$8\ 38 |se| ss] sa| ars S| Kind of Plant. of $3| SS xs SS SS wa S S Experiment.) S2| SR aes $3 | 8° s 2s = PLS anes ce (peal yb tO MPNTWEE 2. 2 < nok on ce os 10 weeks | 1 | 0.337 | 2.140/0.0196 0.0187/—0.0009 oo es en 10.“ 1 | 0.720 | 2.000/0.0322 0 .0325/+-0.0003 1 DT Le eae a 122 “ 1 | 0.748 | 2.847/0.0335 0.0341 |-++0.0006 Tet we ec srate ves 14% 1 | 0.755 | 2.240/0.0339 0 .0329|—0.0010 GUD ee eles ee ane oe he 1.510 | 5.150 Wake NS —0.0010 j 9 « 0810) Sc Beeman 205.500... J sxmanure! 1 | 07300 ¢ 1-730/0.0355 0.0324 —0.0021 10 weeks | 30 : ss MMM Hise Scbic. x0. } poems. ee t 0.100 0.858910. OD48 0.0052'++0.0006 Sum,.4.780 | 16.64/0.2269|0.2240|—0.0035 30 HOW CROPS FEED. Inaccuracy of Ville’s Resulis,—In comparing the in- © : vestigations of Boussingault and Ville as detailed in their — own words, the critical reader cannot fail to be struck © with the greater simplicity of the apparatus used by the : former, and his more exhaustive study of the possible sources of error incidental to the investigation—facts which are greatly in favor of the conclusions of this skillful and ~ experienced philosopher. Furthermore Cloéz, who was employed by a Commission of the French Academy to oversee the repetition of Ville’s experiments, found that a considerable quantity of ammonia was either generated within or introduced into the apparatus of Ville during the period of the trials, which of course vitiated all his results. Any further doubts with regard to this important ae ject have been -effectually disposed of by another most elaborate investigation. Research of Lawes, Gilbert, and Pugh,—In 1857 and 58, the late Dr. Pugh, afterward President of the Penn- sylvania Agricultural College, associated himself with Messrs. Lawes and Gilbert, of Rothamstead, England, for the purpose of investigating all those points con- nected with the subject, which the spirited discussion of the researches of Boussingault and Ville had suggested as possibly accounting for the diversity of their results. Lawes, Gilbert, and Pugh, conducted 27 experiments on graminaceous and leguminous plants, and on buckwheat. The plants vegetated within large glass bells. They were cut off from the external air by the bells dipping into mercury. They were supplied with renewed portions of purified air mixed with carbonic acid, which, being forced into the bells instead of being drawn through them, ef fectually prevented any ordinary air from getting access to the plants. To give an idea of the mode in which these delicate investigations are conducted, we give here a figure and concise description of the appara- ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 31 9.6 30 & 8 32 HOW CROPS FEED. tus employed by Lawes, Gilbert, and Pugh, in their experiments made in the year 1858. A, fig. 5, represents a stone-ware bottle 18 inches in diameter and 24 inches high. _ B, C, and £, are glass 3-necked bottles of about 1 quart capacity. F isa large glass shade 9 inches in diameter and 40 inches high. a represents the cross-section of a leaden pipe, which, passing over all the vessels A of the series of 16, supplied them with water, from a reser- voir not shown, through the tube with stop-cock a b. . ec deisa leaden exit-tube for air. At ¢ it widens, until it enters the vessel A, and another bent tube, g 7 s, passes through it and reaches to the bottom of A, as indicated by the dotted lines. The latter opens at q, and serves as a safety tube to prevent water passing into de. The bottles B C are partly filled with strong sulphuric acid. The tube D D, 1 inch wide and 5 feet long, is filled with fragments of pumice-stone saturated with sulphuric acid, At f/f indentations are made to prevent the acid from draining against the corks with which the tube is stopped. The bottle # contains a saturated solution of pure carbonate of soda. g his a bent and caoutchouc-jointed glass tube connecting the interior of the bottle # with that of the glass shade /% 4k, better indicated in 2, is the exit-tube for air, connecting the interior of the shade # with an eight-bulbed apparatus, Jf, containing sulphuric acid. ww is a vessel of glazed stone-ware, containing mercury in a circular groove, into which the lower edge of the shade F’ is dipped. These glass tubes, gh, wv, and ik, 2, pass under the edge of the shade and communicate with its interior, the mercury cutting off all access of ex- terior air, except through the tubes. Another tube, 2 0, passes air-tight through the bottom of the stone-ware vessel, and thus communicates with its interior. - The tubes wv and 7 & are seen best in 2, which is taken at right angles to 1. The plants were sprouted and grew in pots, v, within the shades. The tube wv was to supply them with water. The water which exhaled from the foliage and gathered on the inside of the shade ran off through 72 0 into the bottle O. This water was re- turned to the pots through wu v. The renewed supply of pure air was kept up through the bottles and tube A, B, C, D, £. On opening the cock a b, A, water enters A, and its pressure forces air through the bottles and tube into the shade F, whence it finds its exit through the tube i &, and the bulb-apparatus JL In its passage through the strong sulphuric acid of B, C, and D, the air is completely freed from ammonia, while the carbonate of soda of # re- moves any traces of nitric acid. The sulphuric acid of the bulb M puri- fies the small amount of air that might sometimes enter the shade through the tube i #, owing to cooling of the air in /, when the current ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 33 was not passing. The outer ends of the tubes ¢ and w were closed with -caoutchouc tubes and glass plugs. In these experiments it was considered advisable to furnish to the plants more carbonic acid than the air contains. This was accomplished by pouring hydrochloric acid from time to time into the bottle 7, which contained fragments of marble. The carbonic acid gas thus liberated joined, and was swept on by the current of airin C. Experiments taught how much hydrochloric acid to add and how often. The proportion of this gas was kept within the limits which previous experimenters had found permissible, and was not allowed to exceed 4.0 per cent, nor to fall below 0.2 per cent. In these experiments the seeds were deposited in a soil purified from nitrogen-compounds, by calcination in a current of air and subsequent washing with pure water. To this soil was added about 0.5 per cent of the ash of the plant which was to growin it. The water used for wa- tering the plants was specially purified from ammonia and nitric acid. The experiments of Lawes, Gilbert, and Pugh, fully confirmed those of Boussingault. For the numerous de- tails and the full discussion of collateral points bearing on the study of this question, we must refer to their elaborate memoir, “ On the Sources of the Nitrogen of Vegetation.” —(Philosophical Transactions, 1861, II, pp. 431-579.) Nitrogen Gas is not Emitted by Living Plants.—It was long supposed by vegetable physiologists that when the foliage of plants is exposed to the sun, free nitrogen is evolved by them in small quantity. In fact, when plants are placed in the circumstances which admit of collecting the gases that exhale from them under the action of light, it is found that besides oxygen a quantity of gas appears, which, unless special precautions are observed, consists chiefly of nitrogen, which was a part of the air that fills the intercellular spaces of the plant, or was dissolved in the water, in which, for the purposes of experiment, the plant is immersed. If, as Boussingault has recently (1865) done, this air be removed from the plant and water, or rather if its quantity be accurately determined and deducted from that obtained in the experiment, the result is that no nitrogen gas remains. A small quantity of gas besides oxygen was indeed usually evolved from the plant when submerged in water. The gas on examination proved to be marsh gas. Cloéz was unable to find marsh gas in the air exhaled from either aquatic or land plants submerged in water, and in his most recent researches (1865) Boussingault found none in the gases given off from the foliage of a living tree examined without submergence. The ancient conclusion of Saussure, Daubeny, Draper, and others, that nitrogen is emitted from the substance of the plant, is thus shown to have been based on an inaccurate method of investigation. Oe 34 HOW CROPS FEED. § 4, RELATIONS OF ATMOSPHERIC WATER TO VEGETABLE NUTRITION. Occurrence of Water in the Atmosphere.—If water be exposed to the air in a shallow, open vessel for some time, | it is seen to decrease in quantity, and finally disappears en- — tirely ; it evaporates, vaporizes, or volatilizes. It is con- verted into vapor. It assumes the form of air, and becomes a part of the atmosphere. The rapidity of evaporation is greater the more eleva- ted the temperature of the water, and the drier the atmos- — phere that is over it. Even snow and ice slowly suffer loss of weight in a dry day though it be frosty. In this manner evaporation is almost constantly going on from the surface of the ocean and all other bodies of water, so that the air always carries a portion of aqueous vapor. On the other hand, a body or mixture whose tempera- ture is far lower than that of the atmosphere, condenses vapor from the air and makes it manifest in the form of water. Thus a glass of ice-water in a warm summer’s day becomes externally bedewed with moisture. In a similar manner, dew deposits in clear and calm summer nights upon the surface of the ground, upon grass, and upon all exposed objects, whose temperature rapidly falls when they cease to be warmed by the sun. Again, when the invisible vapor which fills a hot tea-kettle or steam-boiler issues into cold air, a visible cloud is immediately formed, which consists of minute droplets of water. In like man- ner, fogs and the clouds of the sky are produced by the cooling of air charged with vapor. When the cooling is sufficiently great and sudden, the droplets acquire such size as to fall directly to the ground; the water assumes the form of rain. |? ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 3D Water then exists in the atmosphere during the periods of vegetable activity as gas or vapor,* and as liquid. In the former state it is almost perpetually rising into the air, while in the latter form it frequently falls again to the ground. It is thus in a continual transition, back and forth, from the earth to the sky, and from the sky to the earth. We have given the average quantity of water-vapor in the air at one per cent; but the amount is very variable, and is almost constantly fluctuating. It may range from less than one-half to two and a half or three per cent, ac- cording to temperature and other circumstances. When the air is damp, it is saturated with moisture, so that water is readily deposited upon cool objects. On the other hand, when dry, it is capable of taking up additional moisture, and thus facilitates evaporation. Is Atmospheric Water Absorbed by Plants ?—It has long been supposed that growing vegetation has the power to absorb vapor of water from the atmosphere by its foliage, as well as to imbibe the liquid water which in the form of rain and dew may come in contact with its leaves. Experiments which have been instituted for the purpose of ascertaining the exact state of this question have, how- ever, demonstrated that agricultural plants gather little or no water from these sources. The wilting of a plant results from the fact that the leaves suffer water to evaporate from them more rapidly than the roots can take it up. The speedy reviving of a wilted plant on the falling of a sudden rain or on the depo- sition of dew depends, not so much on the absorption by the foliage, of the water that gathers on it, as it does _ * While there is properly no essential difference between a gas and a vapor, the former term is commonly applied more especially to aériform bodies which are not readily brought to the liquid state, and the latter to those which are easily condensed to liquids or solids. 36 HOW CROPS FEED. on the suppression of evaporation, which is a consequence of the saturation of the surrounding air with water. Unger, and more recently Duchartre, have found, Ist, that plants lose weight (from loss of water) in air that is as nearly as possible saturated with vapor, when their roots are not in contact with soil or liquid water. Du- chartre has shown, 2d, that plants do not gain, but some- times lose weight when their foliage only is exposed to dew or even to rain continued through eighteen hours, al- though they increase in weight strikingly (from absorption of water through their roots,) when the rain is allowed to fall upon the soil in which they are planted. Knop has shown, on the other hand, that leaves, either separate or attached to twigs, gain weight by continued immersion in water, and not only recover what they may have lost by exposure, but absorb more than they orig- inally contained. (Versuchs-Stationen, V1, 252.) The water of dews and rains, it must be remembered, however, does not often thoroughly wet the absorbent sur- face of the leaves of most plants; its contact being pre- vented, to a great degree, by the hairs or wax of the epidermis. Finally, 3d, Sachs has found that even the roots of plants appear incapable of taking up watery vapor. To convey an idea of the method employed in such investigations, we may quote Sachs’ account of one of his experiments. (V. S¢., II,’7.) A young camellia, having several fresh leaves, was taken from the loose soilof the pot inwhich it had been growing; from its long roots all particles of earth were carefully remoy- ed, and its weight was ascertained. The bottom of a glass cylinder was covered with water to a little depth, and the roots of the camellia were introduced, but not in contact with the water. The stem was supported at its ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 37 lower part in a hole in a glass cover,* that was cemented air-tight upon the vessel. The stem itself was cemented by soft wax into the hole, so that the interior of the ves- sel was completely cut off from direct communication with the external atmosphere. The plant thus situated had its roots in an atmosphere as nearly as possible saturated with vapor of water, while its leaves were exposed to the ex- ternal air. After four days had expired, the entire appa- ratus, plant included, had lost 1.823 grm. Thereupon the plant was removed from the vessel and weighed by itself; it had lost 2.188 grm. The loss of the entire apparatus was due to vapor of water, which had escaped through the leaves. The difference between this loss and the loss which the plant had experienced could be attributed only to an exhalation of water through the roots, and amount- ed to (2.188 — 1.823=) 0.365 grm. This exhalation of water into the confined and moist at- mosphere of the glass vessel is explained, according to Sachs, by the fact that the chemical changes proceeding within the plant elevate its temperature above that of the surrounding atmosphere. Knop, in experiments on the transpiration of plants, (V. St., VI, 255,) obtained similar results. He found, however, that a moist piece of paper or wood also lost weight when kept for some time in a confined space over water. He therefore concludes that it is nearly impossible in the conditions of such experiments to maintain the air sat- urated with vapor, and that the loss of weight by the roots is due, not to the heat arising from internal chemical changes, but to simple evaporation from their surface. In one instance he found that a portulacca standing over night in a bell-glass with moistened sides, did not lose, but gained weight, some dew having gathered on its foliage. * The cover consisted of two semicircular pieces of ground glass, each of which had a small semicircular notch, so that the twocould be brought together by their straight edges around the stem. 38 HOW CROPS FEED. The result of these investigations is, that while, perhaps, wilted foliage in a heavy rain may take up a small quan- tity of water, and while foliage and roots may absorb some vapor, yet in general and for the most part the at- mospheric water is not directly taken up to any great ex- tent by plants, and does not therefore contribute immedi- ately to their nourishment. Atmospheric Water Enters Crops through the Soil.— It is only after the water of the atmosphere has become in- corporated with the soil, that it enters freely into agricul- tural plants. The relations of this substance to proper vegetable nutrition may then be most appropriately dis- cussed in detail when we come to consider the soil. (See p. 199.) It is probable that certain air-plants (epiphytes) native to the tropics, which have no connection with the soil, and are not rooted in a medium capable of yielding water, condense vapor from the air in considerable quantity. So also it is proved that the mosses and lichens absorb water largely from moist air, and it is well known that they become dry and brittle in hot weather, recovering their freshness and flexibility when the air is damp. § 5. RELATIONS OF CARBONIC ACID GAS TO VEGETABLE NUTRITION. Composition and Properties of Carbonic Acid, — . When 12 grains of pure carbon are heated to redness in 32 grains of pure oxygen gas, the two bodies unite to- gether, themselves completely disappearing, and 44 grains of a gas are produced which has the same bulk as the oxygen had at the beginning of the experiment. The new gas is nearly one-half heavier than oxygen, and differs in most of its properties from both of its ingredients. It is carbonic acid. This substance is the product of the burn- ing of charcoal in oxygen gas, (H. C. G., p. 35, Exp. 6.) — It is, in fact, produced whenever any organic body is ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 39 burned or decays in contact with the air. It is like oxy- gen, colorless, but it has a peculiar pungent odor and pleasant acid taste. The composition of carbonic acid is evident from what has been said as to its production from carbon and oxygen. It consists of two atoms, or 32 parts by weight, of oxygen, united to one atom, or 12 parts, of carbon. Its symbol is CO,. In the subjoined scheme are given its symbolic, atomic, and percentage composition. At. wt. Per cent. eerie Wal 27.27 Oo = Fs 72.93 CO,. = ..44 100.00 In a state of combination carbonic acid exists in nature in immense quantities. Limestone, marble, and chalk, contain, when pure, 44 per cent of this acid united to lime. These minerals are in chemical language carbonate of lime. Common salratus is a carbonate of potash, and soda- saleratus is a carbonate of soda. From either of these carbonates it is easy to separate this gas by the addition of another and stronger acid. For this purpose we may employ the Rochelle or Seidlitz powders so commonly used in medicine. If we mingle together in the dry state the contents of a blue paper, which contains carbonate of soda, with those of a white paper, which consist of tartaric acid, nothing is observed. If, however, the mixture be placed at the bottom of a tall bottle, and a little water be poured upon it, at once a vigorous bubbling sets in, which is caused by the liberated carbonic acid.* Some important properties of the gas thus set free may be readily made manifest by the following experiments. . a. If a burning taper or match be immersed in the gas, the flame is immediately extinguished. This happens because of the absence of free oxygen. b. If the mouth of the bottle from which carbonic acid is escaping be held to that of another bottle, the gas can be poured into the second ves- sel, on account of its density being one-half greater than that of the air. Proof that the invisible gas has thus been transferred is had by placing * Chalk, marble, or saleratus, and chlorhydric (muriatic) acid, or strong vine- gar (acetic acid) can be equally well employed. 40 HOW CROPS FEED. a burning taper in the second bottle, when, if the experiment was right- ly conducted, the flame will be extinguished. ¢c. Into a bottle filled as in the last experiment with carbonic acid, some lime-water is poured and agitated. The previously clear lime-wa- ter immediately becomes turbid and milky from the formation of earbon- ate of lime, which is nearly insoluble in water. Carbonic Acid in the Atmosphere.—To show the pres- ence of carbonic acid in the atmosphere, it is only neces- sary to expose lime-water in an open vessel. But a little time elapses before the liquid is covered with a white film of carbonate. As already stated, the average proportion of carbonic acid in the atmosphere is 6-10000ths (1-1600th nearly) by weight, or 4—10000ths (1-2500th) by bulk. Its quantity varies somewhat, however. Among over 300 analyses made by De Saussure in Switzerland, Verver in Holland, Lewy in New Granada, and Gilm in Austria, the extreme range was from 47 to 86 parts by weight in 100,000. Deportment of Carbonic Acid towards Water.—W ater dissolves carbonic acid to a greater or less extent, accord- ing to the temperature and pressure. Under the best or- dinary conditions it takes up about its own volume of the gas. At the freezing point it may absorb nearly twice as much, This gas is therefore usually found in spring, well, and river waters, as well as in dew and rain. The consid- erable amount held in solution in cold springs and wells is @ principal reason of the refreshing quality of their wa- ter. Under pressure the proportion of carbonic acid ab- sorbed by water is much larger, and when the pressure is removed, a portion of the gas escapes, resuming its gase- ous form and causing effervescence. The liquid that flows from a soda-fountain is an aqueous solution of carbonic acid, made under pressure, Bottled cider, ale, champagne, and all effervescent beverages, owe their sparkle and much of their refreshing qualities to the carbonic acid they con- tain. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 41 The Absorption of Carbonic Acid by Plants.—In 1771 Priestley, in England, found that the leaves of plants im- mersed in water, sometimes disengaged carbonic acid, sometimes oxygen, and sometimes no gas at all, A few years later Ingenhouss proved that the exhalation of car- bonic acid takes place in the absence, and that of oxygen in the presence, of solar light. Several years more elapsed before Sennebier first demonstrated that the oxygen which is exhaled by foliage in the sunlight comes from the car- bonic acid contained in the water.in which the plants are immersed for the purpose of these experiments. It had been already noticed, by Ingenhouss, that in spring water plants evolve more oxygen than in river water. We now know that the former contains more carbonic acid than the latter. Where the water is by accident or purposely free from carbonic acid, no gas is evolved by foliage in the sunlight. The attention of scientific men was greatly attracted by these interesting discoveries ; and shortly Percival, in England, found that a plant of mint whose roots were stationed in water, flourished better when the air bathing its foliage was artificially enriched in carbonic acid than in the ordinary atmosphere. In 1840 Boussingault furnished direct proof, of what indeed was hardly to be doubted, viz.: the absorption of the carbonic acid of the atmosphere by foliage. Into one of the orifices in a three-necked glass globe he introduced and fixed air-tight the branch of a living vine bearing twenty leaves ; with another opening le connected a tube through which a slow current of air, containing, in one experiment, four-10000ths of carbonic acid, could be passed into the globe, This air after streaming over the vine leaves, at the rate of about 15 gallons per hour, escaped by the third neck into an arrangement for collecting and weighing the carbonie acid that remained in it. The experiment being set in process in the sun- light, it was found that the enclosed foliage removed from the current of air three-fourths of the carbonic acid it at first contained, Influence of the Relative Quantity of Carbonic Acid.— De Saussure investigated the influence of various propor- 42 HOW CROPS FEED. tions of carbonic acid mixed with atmospheric air on the development of vegetation. He found that young peas (4 inches high) when exposed to direct sunlight, endured for some days an atmosphere consisting to one-half of carbonic acid. When the proportion of this gas was increased to two-thirds or more, they speedily withered. In air con- taining one-twelfth of carbonic acid the peas flourished much better than in ordinary atmospheric air. The aver- age increase of each of the plants exposed to the latter for five or six hours daily during ten days was eight grains ; while in the former it amounted in the same time to eleven grains. In the shade, however, Saussure found that increase of the proportion of carbonic acid to one-twelfth was detrimental to the plants. Their growth under these circumstances was but three-fifths of that experienced by similar plants exposed to the same light for the same time, but in common air. He also proved that foliage cannot long exist in the total absence of carbonic acid, when exposed to direct sunlight. This result was obtained by enclosing young plants whose roots were immersed in water, or the branches of trees stationed in the soil, in a vessel which contained moistened quicklime. This substance rapidly absorbs and fixes carbonic acid, forming carbonate of lime, Thus situated, the leaves began in a few days to turn yel- low, and in two to three weeks they dropped off. In darkness the presence of lime not only did not de- stroy the plants, but they prospered the better for its presence, 1. e., for the absence or constant removal of car- bonic acid. : Boussingault has lately shown that pure carbonic acid is decomposed by leaves exposed to sunlight with extreme slowness, or not at all. It must be mixed with some other gas, and when diluted with either oxygen, nitrogen, or hy- drogen, or even when rarefied by the air-pump to a certain extent, the absorption and decomposition proceed as usual. Conclusion, —It thus is proved Ist, that vegetation ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 43 ean flourish only when its foliage is bathed by an atmos- phere which contains a certain small amount of carbonic acid; 2d, that this gas is absorbed by the leaves, and, un- der the influence of sunlight, is decomposed within the plant, its carbon being retained, and in an unknown man- ner becoming a part = the plant itself, while the oxygen is exhaled into the atmosphere in the free state. Relative volumes of absorbed Carbonic Acid and ex- haled Oxygen.—From the numerous experiments of De Saussure, and from similar ones made recently with greatly improved means of research by Unger and Knop, it is es- tablished that in sunlight the volume of oxygen exhaled is nearly equal to the volume of carbonic acid absorbed. Since free oxygen occupies the same bulk as the carbonic acid produced by uniting it with carbon, it is evident that carbon mainly and not oxygen to much extent, is retained by the plant from this source. Respiration and Fixation of Carbon by Plants, —In 1851 Garreau, and in 1858 Corenwinder, reviewed experi- mentally the whole subject of the relations of plants to carbonic acid. Their researches fully confirm the conclu- sions derived from older investigations, and furnish some additional facts. We have already seen (p. 22) that the plant requires free oxygen, and that this gas is absorbed by those parts of vegetation which are in the act of growth. As a con- sequence of this entrance of oxygen into the plant, a cor- responding amount of carbonic acid is produced within and exhales from it. There go on accordingly, in the ex- panding plant, two opposite processes, viz., the absorption of oxygen and exhalation of carbonic acid, and the ab- sorption of carbonic acid and evolution of oxygen. The first process is chemically analogous with the breathing of animals, and may hence be designated as respiration. We may speak of the other process as the fixation of carbon. 44 HOW CROPS FEED. These opposite changes obviously cannot take place at the same points, but must proceed in different organs or cells, or in different parts of the same cells. They further- more tend to counterbalance each other in their effects on the atmosphere surrounding the plant. The processes to which the absorption of oxygen and evolution ofcarbonic acid are necessary, appear to go on at all hours of the day and night, and to be independent of the solar light. The production of carbonic acid is then continually occurring ; but, under the influence of the sun’s direct rays, the oppo- site absorption of carbonic acid and evolution of oxygen proceed so much more rapidly, that when we experiment with the entire plant the first result is completely masked. In our experiments we can, in fact, only measure the pre- ponderance of the latter process over the former. In sun- light it may easily happen that the carbonic acid which exhales from one cell is instantly absorbed by another, and likewise the oxygen, which escapes from the latter, may be in part imbibed by the former. In total darkness it is believed that carbonic acid is not absorbed and decomposed by the plant, but only produced in, and exhaled from it. In no case has any evolution of oxygen been observed in the absence of light. : When, instead of being exposed to the direct rays of the sun, only the diffused light of cloudy days or the soft- ened light of a dense forest acts upon them, plants may, ac- cording to circumstances, exhale either oxygen or carbonic acid in preponderating quantity. In his earlier investiga- tions, Corenwinder observed an exhalation of carbonic acid in diffused light in the cases of tobacco, sunflower, lupine, cabbage, and nettle. On the contrary, he found that let- tuce, the pea, violet, fuchsia, periwinkle, and: others, evolv- ed oxygen under similar conditions. In one instance a bean exhaled neither gas. These differences are not pe- culiar to the plants just specified, but depend upon the in- tensity of the light and the stage of development in which ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 45 the plant exists. Corenwinder noticed that the evolution of carbonic acid in diffused light was best exhibited by very young plants, and mostly ceased as they grew older. Corenwinder has confirmed and extended these observa- tions in more recent investigations. (Ann. d. Sci. Nat., 1864, I, 297.) He finds that buds and young leaves ‘exhale carbonic acid (and absorb oxygen) by day, even in bright sunshine. He also finds that all leaves exhale carbonic acid not alone at night, but likewise by day, when placed in the diffused light of a room, illuminated from only one side. A plant, which in full light yields no carbonic acid to a slow stream of air passing its foliage, immediately gives off the gas when carried into such an apartment, and vice versa. Amount ef Carbonic Acid absorbed.—The quantity of carbonic acid absorbed by day-in direct light is vastly greater than that exhaled during the night. According to Corenwinder’s experiments, 15 to 20 minutes of direct sunlight enable colza, the pea, the raspberry, the bean, and sunflower, to absorb as much carbonic acid as they exhale during a whole night. As to the amount of carbonic acid whose carbon is re- tained, Corenwinder found that a single colza plant took up in one day of strong sunshine more than two quarts of the gas. Boussingault (Comptes Rend., Oct. 23d, 1865) found as the average of a number of experiments, that a square me- ter of oleander leaves decomposed in sunlight 1.108 liters of carbonic acid per hour. In the dark, the same surface of leaf exhaled but 0.07 liter of this gas. Composition of the Air within the Plant.—Full con- firmation of the statements above made is furnished by tracing the changes which take place within the vegeta- ble tissues. Lawes, Gilbert, and Pugh, (PAil. Trans., 1861, II, p. 486,) have examined the composition of the 46 HOW CROPS FEED. air contained in plants, as well when the latter are remoy- ed from, as when they are subjected to, the action of light. To bollset the gas from the plauts, the latter were placed in a glass ressel filled with water, from which all air had been expelled by long boiling and subsequent cooling in full and tightly closed bottles, The vessel was then con- nected with a simple apparatus in which a vacuum was produced by the fall of mercury, down a tube of 30 inches height. The air contained within the cells of the plant was thus drawn over into the vacuum and collected for examination. We give some of the results of the 6th series of their examinations. “The Table shows the Amount and Composition of the Gas evolved into a Tor- ricellian vacuum by duplicate portions of oat-plant, both kept in the dark for some time, and then one exposed to sunlight for about twenty minutes, when both were sub- mitted to exhaustion.” | Per cent. Wake Conditions | Cubic centimeters 1858. during of Nitrogen.| Oxygen.| Carbonic Acid. ‘| Hahaustion. Gas collected. In dark. 24.0 77.08 3.75 TO OUG July 31. iin sunlight. 34.5 68.69 | 24.93 6.38 Aue. 12 §In dark. 10.6 68.28 10.21 21.51 5° “*)) In sunlight. 39.2 67.86 25.95 6.89 Nene OO) In dark. 30.7 76.87 8.14 14.99 ug. “-/) In sunlight. 26.5 69.43 | 27.17 3.40 These analyses show plainly what it is that happens in the cells of the plant. The atmospheric air freely pene- trates the vegetable tissues, (H. C. G., p. 288.) In dark- ness, the oxygen that is thus contained within the plant . takes carbon from the vegetable matter and forms with it carbonic acid. This process goes on with comparative rapidity, and the proportion of oxygen may be diminish- ed from 21, the normal percentage, to 4, or even, as in some other experiments, to less than 1 per cent of the volume of the air. Upon bringing the vegetable tissue into sunlight, the carbonic acid previously formed within the cells undergoes decomposition. with separation of its ATMOSPHERIC AIR AS THE FOOD OF PLANTS, AY oxygen in the free gaseous condition, while its carbon re- mains in the solid state as a constituent of the plant. Re- ferring to the table above, we see that twenty minutes’ exposure to the solar rays was sufficient in the second ex- periment (where the proportion of nitrogen remained nearly unaltered) to decompose 14 per cent of carbonic acid and liberate its oxygen. The total volume of air collected was 2.4 cubic inches, and the volume of decomposed car- bonic acid was 4 of a cubic inch, that of the liberated oxygen being the same. Supply of Carbonic Acid in the Atmosphere.—Although this body forms but rsa55 of the weight of the atmosphere, yet such is the immense volume of the latter that it is cal- culated to contain, when taken to its entire height, no less than 3,400,000,000,000 tons of carbonic acid. This amounts to about 28 tons over every acre of the earth’s surface. According to Chevandier, an acre of beech-forest annu- ally assimilates about one ton (1950 lbs.) of carbon, an amount equivalent to 33 tons of this gas. Were the whole earth covered with this kind of forest, and did it depend solely upon the atmosphere for carbon, eight years must elapse before the existing supply would be exhausted, in case no means had been provided for restoring to the air what vegetation constantly removes. When we consider that but one-fourth of the earth’s surface is land, and that on this the annual vegetable pro- duction is very far below (not one-third) the amount stat- ed above for thrifty forest, we are warranted in assuming the atmospheric content of carbonic acid sufficient, with- out renewal, fora hundred years of growth. This ingredi- ent of the atmosphere is maintained in undiminished quantity by the oxidation of carbon in the slow decay of organic matters, in the combustion of fuel, and in animal respiration. That the carbonic acid of the atmosphere may fully suf- 48 HOW CROPS FEED fice to provide a rapidly growing vegetation with carbon is demonstrated by numerous facts. Here we need only mention that in a soil totally destitute of all carbon, be- sides that contained in the seeds sown in it, Boussingault brought sunflowers toa normal development. The writer has done the same with buckwheat; and Sachs, Knop, Stohmann, Nobbe and Siegert, and others, have produced perfect plants of maize, oats, etc., whose roots, throughout the whole period of growth, were immersed in a weak, saline solution, destitute of carbon, (See H. C. G., Water Culture, p. 167.) Hellriegel’s recent experiments give the result that the atmospheric supply of carbonic acid is probably sufficient for the production of a maximum crop under all cireum- stances; at least artificial supply, whether of the gas, of its aqueous solution, or of a carbonate, to the soil, had no effect to increase the crop. (Chem. Ackersmann, 1868, p- 18.) Liebig considers carbonic acid to be, under all cireum- stances, the exclusive source of the carbon of agricultural. vegetation. To this point we shall recur in our study of the soil. Carbon fixed by Chlorophyll.—The fixation of carbon from the carbonic acid of the air is accomplished in, or has an intimate relation with, the chlorophyll graims of the leaf or green stem. This is not only evident from the microscopic study of the development of the carbohy- drates, especially starch, whose organization proceeds from the chlorophyll, but is an inference from the experiments of Gris on the effects of withholding iron from plants. In absence of iron, the leaf may unfold and attain a certain development; but chlorophyll is not formed, and the plant soon dies, without any real growth by assimilation of food from without. (H. C. G, p. 200.) Finally, experiment shows that oxygen is given off (and carbonic acid decom- posed with fixation of carbon) only from those parts of - i= * ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 49 plants in which the microscope reveals chlorophyll, although _ the prevailing color may be other than green. Influence of Light on Fixation of Carbon.—As men- tioned, Ingenhouss (in 1779) discovered, that oxygen gas is given off from foliage, and carbon fixed in the plant _ only under the influence of light. Experiments show that when a seed germinates in exclusion of light it not only does not gain, but steadily loses weight from the consump- tion of carbon (and hydrogen) in slow oxidation (respira- tion). Thus Boussingault (Comptes Rendus, 1864, p. 883) caused two beans to germinate and vegetate, one in the ordinary light and one in darkness, during 26 days. The gain in light and loss in darkness in entire (dry) weight, and of carbon, etc., are seen from the statement below. In Light. In Darkness. Weight of seed...... RE SPAM ics Faas Sy Saks 0.926 gram. Weight of plant..... iS 5 Cm Serer © 0.566 “* Gain = 0.371 gram. Loss....0.360 gram. Carbon, Gain =» 0.1926 - * Loss...0.1598 ‘ Hydrogen, ‘© = 0.0200 ‘* £0 ne GORaa"~ = Rrapeet 8S == O1591 . © OG § 6. THE AMMONIA OF THE ATMOSPHERE AND ITS RELATIONS TO VEGETABLE NUTRITION, _ Ammonia is a gas, colorless and invisible, but having a peculiar pungency of odor and an acrid taste. Preparation.—It may be obtained in a state of purity by heat- ing a mixture of chloride of ammonium (sal ammoniac) and quicklime. Equal quantities of the two substances just named (50 grams of each) are separately pulverized, introduced into a flask, and well mixed by shaking. A straight tube 8 inches long is now secured in the neck of the flask by means of a perforated cork, and heat applied. The ammonia gas which soon escapes in abundance is collected in dry bottles, which are inverted over the tube. The gas, rapidly entering the bottle, ina few moments displaces the twice heavier atmospheric air. As soon asa 3 50 HOW CROPS FEED. feather wet with vinegar or dilute chlorhydric acid becomes surrounded with a dense smoke when approached to the mouth of the bottle, the latter may be removed, corked, and another put in its place. Three or four pint bottles of gas thus collected will serve to illustrate its proper- ties, as shortly to be noticed. Solubility in Water.—This character of ammonia is ex- hibited by removing, under cold water, the stopper of a bottle filled with the gas. The water rushes with great — violence into the bottle as into a vacuum, and entirely fills it, provided all atmospheric air had been displaced. The agua ammonia, or spirits f hartshorn of the drug- ; gist, is a strong solution of ammonia, prepared by passing — a stream of ammonia gas into cold water. At the freez- — ing point, water absorbs 1,150 times its bulk of ammonia. | When such a solution is warmed, the gas escapes abund- antly, so that, at ordinary summer temperatures, only one- — half the ammonia is retained. If the solution be heated — to boiling, all the ammonia is expelled before the water has nearly boiled away. The gas escapes even from very di- lute solutions when they are exposed to the air, as is at once recognized by the sense of smell. Composition.— When ammonia gas is heated to redness by being made to pass through an ignited tube, it 1s de- composed, loses its characteristic odor and other proper- ties, and is resolved into a mixture of nitrogen and hydro- gen gases. These elements exist in ammonia in the pro- portion of one part by bulk of nitrogen, to three parts of hydrogen, or by weight fourteen parts or one atom of nitrogen and three parts, or three atoms of hydrogen. The subjoined scheme exhibits the composition of ammo- nia, as expressed in symbols, atoms, and percentages. Symbol. At. w't. Per cent. N a | er es 82.39 i. oe = Babancas 17.61 NUS > fie LT Eg Formation of Ammonia.—1. When hydrogen and ni- trogen gases are mingled together in the proportions to ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 51 form ammonia, they do not combine either spontaneously or by aid of any means yet devised, but remain for an indef- inite period as a mere mixture. The oft repeated assertion that nascent hydrogen, i. e., hydrogen at the moment of liberation from some combination, may unite with free nitrogen to form ammonia, has been completely refuted by the experiments of Will, (Ann. Ch. u. Ph., XLV, 110.) The ammonia observed by older experimenters existed, ready formed, in the materials they operated with. 2. It appears from recent researches (of Boettger, Schénbein, and Zabelin) that ammonia is formed in minute quantity from atmospheric nitrogen in many cases of com- bustion, and is also generated when vapor of water and the air act upon each other in contact with certain organic matters, at a temperature of 120° to 160° F. To this sub- ject we shall again recur. p. 77. 3. Ammonia may result from the reduction of nitrous and nitric acids, and from the action of alkalies and lime upon the albuminoids, gelatine, and other similar organic matters. To these modes of its formation we shall recur on subsequent pages. 4, Ammonia is most readily and abundantly formed from organic nitrogenous bodies; e. g., the albuminoids and similar substances, by decay or by dry distillation. It is supposed to have been called ammonia because one of its most common compounds (sal ammoniac) was first prepared by burning camels’ dung near the temple of Jupiter Ammon in Libya, Asia Minor. The name hartshorn, or spirits of hartshorn, by which it is more commonly known, was adopted from the circumstance of its preparation by dis- tilling the horns of the stag or hart. The ammonia and ammoniacal salts of commerce (car- bonate of ammonia, sal ammoniac, and sulphate of ammo- nia) are exclusively obtained from these sources, - When trine is allowed to become stale, it shortly smells 52 HOW CROPS FEED. of ammonia, which copiously escapes in the form of car- bonate, and may be separated by distillation. When bones are heated in close vessels, as in the manu- — facture of bone-black or bone-char for sugar refining, the liquid product of the distillation is sitonaly charged with carbonate of ammonia. Commercial ammonia is mostly derived, at present, from the distillation of bituminous coal, and is a bye-product of the manufacture of illuminating gas. The gases and va- pors that issue from the gas-retort in which the coal is heat- ed to redness, are washed by passing through water. This wash water is always found to contain a small quantity of ammonia, which may be cheaply utilized The exhalations of volcanoes and fumeroles likewise contain ammonia, which is probably formed in a similar manner. In the processes of combustion and decay the elements of the organic matters are thrown into new groupings, which are mostly simpler in composition than the original substances. A portion of nitrogen and a corresponding portion of hydrogen then associate themselves to form am- monia. . Ammonia is a Strong Alkaline Base.—Those bases. which have in general the strongest affinity for acids, are potash, soda,and ammonia. These bodies are very similar in many of their most obvious characters, and are collec- tively denominated the alkalies. They are alike freely soluble in water, have a bitter, burning taste, alike corrode the skin and blister the tongue; and, united with acids, form the most permanent saline compounds, or salts. Carbonate of Ammonia.—lIf a bottle be filled with car- bonic acid, (by holding it inverted over a candle until the latter becomes extinguished when passed a little way into the bottle,) and its mouth be applied to that of a vessel containing ammonia gas, the two invisible airs at once ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 53 combine to a solid salt, the carbonate of ammonia, which appears as a white cloud where its ingredients come in contact. Carbonate of ammonia occurs in commerce under the name “salts of hartshorn,” and with the addition of some perfume forms the contents of the so-called smelling-bot- tles. It rapidly vaporizes, exhaling the odor of ammonia very strongly, and is hence sometimes termed sal volatile. Like camphor, this salt passes from the solid state into that of invisible vapor, at ordinary temperatures, without assuming intermediately the liquid form. In the atmosphere the quantity of carbonic acid greatly preponderates over that of the ammonia; hence it is im- possible that the latter should exist in the free state, and we must assume that it occurs there chiefly in combination with carbonic acid. The carbonate of ammonia, whether solid or gaseous, is readily soluble in water, and like free ammonia it evaporates from its solution with the first portions of aqueous vapor, leaving the residual water rel- atively free from it. In the guano-beds cf Peru and Bolivia, carbonate of ammonia is sometimes found in the form of large trans- parent crystals, which, like the artificially-prepared salt, rapidly exhale away in vapor, if exposed to the air. This salt, commonly called bicarbonate of ammonia, con- tains in addition to carbonic acid and ammonia, a portion of water, which is indispensable to its existence. Its com- position is as follows: - Symbot. Af. w't. Per cent. NH; 17 21.5 H,O 18 22.8 CO. 44 55.7 NH3;. H,0. CO, 79 100.0 Tests for Ammonia.—a. If salts of ammonia are rubbed to- gether with slaked lime, best with the addition of a few drops of water, the ammonia is liberated in the gaseous state, and betrays itself (1) by its characteristic odor ; (2) by its reaction on moistened test-papers ; and 54 _ HOW ‘CROPS FEED. (3) by giving rise to the formation of white fumes, when any object (e. %, a glass rod) moistened with hydrochloric acid, is brought in contact with it. These fumes arise from the formation of solid ammoniacal salts pro- duced by the contact of the gases. b. Nessler’s Test.—For the detection of exceedingly minute (iors of ammonia, a reaction first pointed out by Nessler may be employed. Di- gest at a gentle heat 2 grammes of iodide of potassium, and 3 grammes of iodide of mercury, in 5 cub. cent. of water; add 20 cub. cent. of wa- — ter, let the mixture stand for some time, then filter; add to the filtrate 30 cub. cent. of pure concentrated cote of potassa(1 : 4); and, should — a precipitate form, filter again. If to this solution is added, in small quantity, a liquid SoneAraine ammonia oran ammonia-salt, a reddish brown precipitate, oy with exceedingly small quantities of ammonia, a yellow coloration is produced from the formation of dimercurammonic iodide, NHg. I.0Hg. c. Bohlig’s Test.—According to Bohlig, chloride of mercury (corrosive sublimate) is the most sensitive reagent for ammonia, when in the free state or as carbonate. It gives a white precipitate, or in very dilute so- lutions (even when containing but |900,000 of ammonia) a white turbidity, due to the separation of mercurammonic chloride, NHg Hg.Cl. In solu- tions of the salts of ammonia with other acids than carbonic, a clear solution of mixed carbonate of potassa and chloride of mercury must be employed, which is prepared by adding 10 drops of a solution of the purest carbonate of potassa, (1 of salt to 50 of water,) and 5 drops of a solution of chloride of mercury to 80 c. c. of water exempt from am- monia (such is the water of many springs, but ordinary distilled water rarely). This reagent may be kept in closed vessels for a time without change. If much more concentrated, oxide of mercury separates from it. By its use the ammonia salt is first converted into carbonate by double decomposition with the carbonate of potassa, and the further reaction proceeds as before mentioned. Occurrence of Ammonia in the Atmosphere.—The ex- istence of ammonia in the atmosphere was first noticed by De Saussure, and has been proved repeatedly by direct experiment. That the quantity is exceedingly minute has been equally well established. Owing partly to the variable extent to which ammonia occurs in the atmosphere, but chiefly to the difficulty of collecting and estimating such small amounts, the siate- ments of those who os experimented upon thig subject are devoid of agreement. We present here a tabulated view of the most trust- worthy results hitherto published: ee ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 55 1,000,000,000 parts of atmospheric air contain of ammonia, according to Graeger, at Mihlhausen, Germany, average, 333 parts. Fresenius, ‘‘ Wiesbaden, oe oe oar: gs Pierre, “ Caen, France, 1851-52, UL: 3100) 0 men (79 ce ce ac 1852-53, cc 500 a4 Bineau, ‘“‘Lyons, ‘* 1852-53, ci 290; <8 ke “Caluire, ‘* “winter, 40. ‘ a9 ¢ ‘ ‘ (74 cc , i : summer, 80 Ville, (Paris; ¥ 1849-50, average, 24 ‘ oF “a Greets. " 1851, ae P| Graham has shown by experiment (Ville, Hest ches sur la Vegetation, Paris, 1853, p. 5,) that a quantity of ammonia like that found by Fresenius is sufficient to be readily detected by its effect on a red litmus paper, which is not altered in the air. This demonstrates that the at- mosphere where Graham experimented (London) contained less than **| | jso.0o0thS Of ammonia in the state of bicar- bonate. The experiments of Fresenius and of Griger were made with comparatively small volumes of air, and those of the latter, as well as those of Pierre, and some of Bineau’s, were made in the vicinity of dwellings, or even - in cities, where the results might easily be influenced by local emanations. Bineau’s results were obtained by a method scarcely admitting of much accuracy. The investigations of Ville (Recherches, Paris, 1853,) are, perhaps, the most trustworthy, having been made on a large scale, and apparently with every precaution. We may accordingly assume that the average quantity of am- monia in the air is one part in fifty millions, although the amount is subject to considerable fluctuation. From the circumstance that ammonia and its carbonate are so readily soluble in water, we should expect that in rainy weather the atmosphere would be washed of its am- monia; while after prolonged dry weather it would con- tain more than usual, since ammonia escapes from its solutions with the first portions of aqueous vapor. The Absorption of Ammonia by Vegetation.—The gen- eral fact that ammonia in its compounds is appropriated 56 HOW CROPS FEED by plants as food is most abundantly established. The salts of ammonia applied as manures in actual farm prac- tice have produced the most striking effects in thongands of instances. . By watering potted plants with very dilute solutions of © ammonia, their luxuriance is made to surpass by far that of similar plants, which grow in precisely the same condi- tions, save that they are supplied with simple water. | Ville has stated, 1851-2, that vegetation in conserva- tories may be remarkably promoted by impregnating the — air with gaseous carbonate of ammonia. For this purpose — lumps of the solid salt are so disposed on the heating ap- paratus of the green-house ag to gradually vaporize, or — vessels containing a mixture of quicklime and sal ammo- niac may be employed. Care must be taken that the air does not contain at any time more than four ten-thousandths of its weight of the salt; otherwise the foliage of tender plants isinjured. Like results were obtained by Petzholdt and Chlebodarow in 1852-3. Absorption of Ammonia by Foli- — age.—Although such facts indicate — that ammonia is directly absorbed by foliage, they fail to prove that the soil is not the medium through which the absorption really takes place. We remember that according to Unger and Duchartre water enters the higher plants almost exclusively by the roots, after it has been absorbed by the soil, To Peters and Sachs (Chem. Ackersmann, 6, 158) we owe an experiment which appears to de- monstrate that ammonia, like carbonic acid, is imbibed by the leaves of Vig. 6. plants. The figure represents the ap- paratus employed. It consisted of a glass bell, resting below, ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 5 air-tight, upon a glass plate, and having two glass tubes cemented into its neck above, as in fig. 6. Through an aperture in the centre of the glass plate the stem of the plant experimented on was introduced, so that its fo- liage should occupy the bell, while the roots were situated in a pot of earth beneath. Two young bean-plants, grow- ing in river sand, were arranged, each in a separate appa- ratus, as in the figure, on June 19th, 1859, their stems be- ing cemented tightly into the opening below, and through the tubes the foliage of each plant received daily the same quantities of moist atmospheric air mixed with 4-5 per cent of carbonic acid. One plant was supplied in addition with a quantity of carbonate of ammonia, which was in- troduced by causing the air that was forced into the bell to stream through a dilute solution of this salt. Both plants grew well, until the experiment was terminated, on the 11th of August, when it was found that the plant whose foliage was not supplied with carbonate of ammo- nia weighed, dry, 4.14 gm., while the other, which was supplied with the vapor of this salt, weighed, dry, 6.74 gms. The first plant had 20 full-sized leaves and 2 side shoots; the second had 40 leaves and 7 shoots, besides a much larger mass of roots. The first contained 0.106 gm. of nitrogen; the second, double that amount, 0.208 gm. Other trials on various plants failed from the diff- culty of making them grow in the needful circumstances. The absorption of ammonia by foliage does not appear, like that of carbonic acid, to depend upon the action of sunlight; but, as Mulder has remarked,* may go on at all times, especially since the juices of plants are very fre- quently more or less charged with acids which directly unite chemically with ammonia. - When absorbed, ammonia is chiefly applied by agricul- * Chemie der Ackerkrume, Vol. 2, p. 211. 3% 58 HOW CROPS FEED. tural plants to the production of the albuminoids.* We measure the nutritive effect of ammonia salts applied as fertilizers by the amount of nitrogen which vegetation as- similates from them. Effects of Ammonia on Vegetation. — The remarkable effect of carbonate of ammonia upon vegetation is well described by Ville. We know that most plants at a cer- tain period of growth under ordinary circumstances cease to produce new branches and foliage, or to expand those already formed, and begin a new phase of development in providing for the perpetuation of the species by producing flowers and fruit. If, however, such plants are exposed to as much carbonate of ammonia gas as they are capable of enduring, at the time when flowers are beginning to form, these are often totally checked, and the activity of growth is transferred to stems and leaves, which assume anew vigor and multiply with extraordinary luxuriance. If flowers are formed, they are sterile, and yield no seed. Another noticeable effect of ammonia—one, however, which it shares with other substances—is its power of deep- ening the color of the foliage of plants. This is an indi- cation of increased vegetative activity and health, as a pale or yellow tint belongs to a sickly or ill-fed growth. A third result is that not only the mass of vegetation is increased, but the relative proportion of nitrogen in it is heightened. This result was obtained in the experiment of Peters and Sachs just described. To adduce a single other instance, Ville found that grains of wheat, grown in pure air, eontained 2.09 per cent of nitrogen, while those which were produced under the influence of ammonia contained 3.40 per cent. * In tobacco, to the production of nicotine ; in coffee, of caffeine; and inmany other plants to analogous substances. Plants appear oftentimes to contain small quantitées of ammonia salts and nitrates, as well as of asparagin, (C4 Hg Ne O3,)a substance first found in asparagus, and which is formed in many plants when they vegetate in exclusion of light. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59 Do Healthy Plants Exhale Ammonia !—The idea having been advanced that in the act of vegetation a loss of ni- trogen may occur, possibly in the form of ammonia, Knop made an experiment with a water-plant, the Typha lati- folia, a species of Cat-tail, to determine this point. The plant, growing undisturbed in a pond, was enclosed in a glass tube one and a half inches in diameter, and six feet long. The tube was tied to a stake driven for the purpose ; its lower end reached a short distance below the surface of the water, while the upper end was covered air-tight with a cap of India rubber. This cap was penetrated by a narrow glass tube, which communicated with a vessel ; filled with splinters of glass, moistened with pure hydro- chloric acid. As the large tube was placed over the plant, a narrow U-shaped tube was immersed in the water to half its length, so that one of its arms came within, and the other without, the former. To the outer extremity of the U-tube was attached an apparatus, for the perfect absorption of ammonia. By aspirating at the upper end of the long tube, a current of ammonia-free air was thus made to enter the bottom of the apparatus, stream upward along the plant, and pass through the tube of glass-splint- ers wet with hydrochloric acid. Were any ammonia evolved within the long tube, it would be collected by the acid last named. To guard against any ammonia that possibly might arise from decaying matters in the water, a thin stratum of oil was made to float on the water with- in the tube. Through this arrangement a slow stream of air was passed for fifty hours. At the expiration of that time the hydrochloric acid was examined for ammonia; but none was discovered. Our tests for ammonia are so delicate, that we may well assume that this gas is not ex- haled by the Zypha latifolia. The statements to be found in early authors (Sprengel, Schiibler, Johnston), to the effect that ammonia is exhaled. by some plants, deserve further examination. 60 HOW CROPS FEED. . The Chenopodium vulvaria exhales from its foliage a — body chemically related to ammonia, and that has been mistaken for it. This substance, known to the chemist as — trimethylamine, is also contained in the flowers of Cra- — tegus oxycantha, and is the cause of the detestable odor of these plants, which is that of putrid salt fish.* (Wagke, ‘Liebig’s Ann., 124, p. 338.) Certain fined (toad-stools) emit trimethylamine, or some analogous compound. (Lehmann, Sachs’ Lxperimentaé Physiologie der Pflanzen, p. 273, note.) It is not impossible that ammonia, also, may be exhaled from these plants, but we have as yet no proof that such is the case. Ammonia of the Atmospheric Waters.—The ammonia proper to the atmosphere has little effect upon plants through their foliage when they are sheltered from dew and rain. Such, at least, is the result of certain experi- ments. Boussingault (Agronomie, Chimie Agricole, et Physt- ologie, T. I, p. 141) made ten distinct trials on lupins, beans, oats, wheat, and cress. The seeds were sown in a soil, and the plants were watered with water both exempt from nitrogen. The plants were shielded by glazed eases from rain and dew, but had full access of air. The result of the ten experiments taken together was as follows: Weight of needs... ..... ..<0,'ss5 4.965 grm’s. = “dry harvest. «5.2... 18.730 “ Nitrogen in harvest and soil.. .2499 as SSIES a Penns dines 5: Vy ai Gain of nitrogen..... .0192 grm’s = 7.6 per cent of the total quantity. When rains fall, or dews deposit upon the surface of the * Trimethylamine C3H9N = N (CH3)3 may be viewed as ammonia NH sg, in which the three atoms of hydrogen are replaced by three atoms of methyl CHs. It isa gas like ammonia, and has its pungency; but accompanied with the odor of stale fish. It is prepared from herring pickle, and used in medicine un- der the name propylamine. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 61 soil, or upon the foliage of a cultivated field, they bring down to the reach of vegetation in a given time a quantity of ammonia, far greater than what is diffused throughout the limited volume of air which contributes to the nour- ishment of plants. The solubility of carbonate of ammo- nia in water has already been mentioned. In a rain-fall we have the atmosphere actually washed to a great de- gree of its ammonia, so that nearly the entire quantity of this substance which exists between the clouds and the earth, or in that mass of atmosphere through which the rain passes, is gathered by the latter and accumulated within a small space. Proportion of Ammonia in Rain-water, etc.—The pro- portion of ammonia * which the atmospheric waters thus collect and bring down upon the surface of the soil, or upon the foliage of plants, has been the subject of inves- tigations by Boussingault, Bineau, Way, Knop, Bobiere, and Bretschneider. The general result of their accordant investigations is as follows: In rain-water the quantity of ammonia in the entire fall is very variable, ranging in the country from 1 to 33 parts in 10 million. In cities the amount is larger, tenfold the above quantities having been observed. The first portions of rain that fall usually contain much more ammonia than the latter portions, for the reason that a certain amount of water suffices to wash the air, and what rain subsequently falls only dilutes the solution at first formed. In a long-continued rain, the water that finally falls is almost devoid of ammonia. In rains of short duration, as well as in dews and fogs, which occasion- ally are so heavy as to admit of collecting to a sufficient extent for analysis, the proportion of ammonia is greatest, and is the greater the longer the time that has elapsed since a previous precipitation of water. * In all quantitative statements regarding ammonia, NH3 is to be understood, and not NH40O. 62 3 HOW CROPS FEED. Boussingault found in the first tenth of a slow-falling rain (24th Sept., 1853) 66 parts of ammonia, in the last three-tenths but 13 parts, to 10 million of water. In dew he found 40 to 62; in fog, 25 to 72; and in one extraordi- nary instance 497 parts in ten million. Boussingault found that the average proportion of am- monia in the atmospheric waters (dew and fogs included) which he was able to collect at Liebfrauenberg (near Stras- burg, France) from the 26th of May to the 8th of Nov. 1853, was 6 parts in 10 million (Agronomie, etc., T. II, 238). Knop found in the rains, snow, and hail, that fell at Moeckern, near Leipzig, from April 18th to Jan. 15th, 1860, an average of 14 parts in 10°million. (Versuchs- Stationen, Vol. 3, p. 120.) Pincus and Rollig obtained from the atmospheric wa- ters collected at Insterburg, North Prussia, during the 12 months ending with March, 1865, in 26 analyses, an average of 7 parts of ammonia in 10 million of water. The average for the next following 12 months was 9 parts in 10 million. Bretschneider found in the atmospheric waters collected by him at Ida-Marienhiitte, in Silesia, from April, 1865, to April, 1866, as the average of 9 estimations, 30 parts of ammonia in 10 million of water. In the next year the quantity was 23 parts in 10 million. In 10 million parts of rain-water, ete., collected at the following places in Prussia, were contained of ammonia— at Regenwalde, in 1865, 24; in 1867, 28; at Dahme, in 1865, 17; at Kuschen, in 1865,545; and in 1866, 73 parts. (Preus. Ann. d. Landwirthschaft, 1867.) ‘The monthly averages fluctuated without regularity, but mostly within narrow limits. Occasionally they fell to 2 or 3 parts, once to nothing, and rose to 35 or 40, and once to 144 parts in 10 million. Quantity of Ammonia per Acre Brought Down by Rain, etc.—In 1855 and 756, Messrs. Lawes & Gilbert, at Roth- amstead, England, collected on a large rain-gauge having a Se ee eee. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 63 a surface of 3950 of an acre, the entire rain-fall (dews, etc., included) for those years. Prof. Way, at that time chem- ist to the Royal Ag. Soc. of England, analyzed the waters, and found that the total amount of ammonia contained in them was equal to 7 lbs. in 1855, and 94 lbs. in 1856, for an acre of surface. These amounts were yielded by 663,000 and 616,000 gallons of rain-water respectively. In the waters gathered at Insterburg during the twelve- month ending March, 1865, Pincus and Rdllig obtained 6.38 lbs. of ammonia per acre., Bretschneider found in the waters collected at Ida-Ma- rienhiitte from April, 1865, to April, 1866, 12 lbs. of am- monia per acre of surface. The significance of these quantities may be most appro-_ priately discussed after we have noticed the nitric acid of the atmosphere, a substance whose functions towards vege- tation are closely related to those of ammonia. § 7. OZONE. When lightning strikes the earth or an object near its surface, a person in the vicinity at once perceives a peculiar, so-called “ sulphureous” odor, which must belong to something developed in the atmosphere by electricity. The same smell may be noticed in a room in which an electrical machine has been for some time in vigorous action. The substance which is thus produced is termed ozone, froma Greek word signifying to smell. It is a colorless gas, possessing most remarkable properties, and is of the highest importance in agricultural science, although our knowledge of it is still exceedingly imperfect. Ozone is not known in a pure state free from other bodies; but hitherto has only been obtained mixed with 64 HOW CROPS FEED. several times its weight of air or oxygen.* It is entirely insoluble in water. It has, when breathed, an irritating action on the lungs, and excites coughing like chlorine gas. Small animals are shortly destroyed in an atmosphere charged with it. It is itself instantly destroyed by a pee considerably below that of redness. The special character of ozone that is of hie, in connection with questions of agriculture is its oxidizing power. Silver isa metal which totally refuses to combine with oxygen under ordinary circumstances, as shown by its maintaining its brilliancy without symptom of rust or tarnish when exposed to pure air at common or at greatly elevated temperatures. When a slip of moistened silver is placed in a vessel the air of which is charged with ozone, the metal after no long time becomes coated with a black crust, and at the same time the ozone disappears. By the mp plieatinn of a gentle heat to the blackened silver, ordinary oxygen gas, having the properties already mentioned as belonging to this element, escapes, and the slip recovers its original silvery color. The black crust is in fact an oxide of silver (AgO,) which readily suffers de- composition by heat. In a similar manner iron, copper, lead, and other metals, are rapidly oxidized. A variety of vegetable pigments, such as indigo, litmus, ete., are speedily bleached by ozone. This action, also, is simply one of oxidation. Gorup-Besanez (Ann. Ch. u. Ph., 110, 86; also, Physiologische Chemie) has examined the deportment of a number of organic bodies towards ozone. He finds that egg-albumin and casein of milk are rapidly altered by it, while flesh fibrin is unaffected. Starch, the sugars, the organic acids, and fats, are, when pure, unaf- fected by ozone. In presence of (dissolved in) alkalies, however, they are Oxidized with more or less rapidity. It is remarkable that oxidation by ozone takes place only in the pm esence of water, Dry substances are unaffected by it. The peculiar deportment towards ozone of certain volatile oils will be presently noticed. * Babg and Claus (Ann. Ch. u. Ph., 2d Sup., p. 804) prepared a mixture of oxy- gen and ozone containing nearly 6 per cent of the latter. ~* ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 65 Tests for @zome.—Certain phenomena of oxidation that are attended with changes of color serve for the recognition of ozone. We havealready seen (H. C. G.,p. 64) that starch, when brought in contact with iodine, at once assumes a deep blue or purple color. When the compound of iodine with potassium, known as iodide of potas- sium; is acted on by ozone, its potassium is at once oxidized (to pot- ash,) and the iodine is set free. If now paper be impregnated with a mixture of starch-paste and solution of iodide of potassium,* we have a test of the presence of ozone, at once most characteristic and delicate. Such paper, moistened and placed in ozonous f air, is speedily turned blue by the action of the liberated iodine upon the starch. By the use of this test the presence and abundance of ozone in the atmosphere has been measured. Ozone is Active Oxygen.—That ozone is nothing more or less than oxygen in a peculiar, active condition, is shown by the following experiment. When perfectly pure and dry oxygen is enclosed ina glass tube containing moist metallic silver in a state of fine division, it is possible by long-continued transmission of electrical discharges to cause the gaseous oxygen entirely to disappear. On heat- ing the silver, which has become blackened (oxidized) by the process, the original quantity of oxygen is recovered in its ordinary state. The oxygen is thus converted under the influence of electricity into ozone, which unites with the silver and disappears in the solid combination. The independent experiments of Andrews, Babo, and Soret, demonstrate that ozone has a greater density than oxygen, since the latter diminishes in volume when elec- trized. Ozone is therefore condensed oxygen, i. e., its molecule contains more atoms than the molecule of ordi- nary oxygen gas. * Mix 10 parts of starch with 200 parts of cold water and 1 part of recently fused iodide of potassium, by rubbing them together in amortar; then heat to boiling, and strain through linen. Smear pure filter paper with this paste, and dry The paper should be perfectly white, and must be preserved in a well-stoppered bottle. + I. e., charged with ozone. t Recent observations by Babo and Claus, and by Soret, show that the density of ozone is one and a half times greater than that of oxygen. 66 HOW CROPS FEED. Allotropism.—tThis occurrence of an element in two or even more forms is not without other illustrations, and is termed Allotropism. Phosphorus occurs in two conditions, viz., red phosphorus, which erys- tallizes in rhomboledrons, and like ordinary oxygen is comparatively inactive in its affinities; and colorless phosphorus, which crystallizes in octahedrons, and, like ozone, has vigorous tendencies to unite with other bodies. Carbon is also found in three allotropic forms, viz., diamond, plumbago, and charcoal, —— differ exceedingly in their chemical and physical characters. Ozone Formed by Chemical Action.—N ot onlp-is is ozone produced by electrical disturbance, but it has likewise been shown to originate from chemical action; and, in fact, from the very kind of action which it itself so vig- orously manifests, viz., oxidation. When a clean stick of colorless phosphorus is placed at the bottom of a large glass vessel, and is half covered with tepid water, there immediately appear white vapors, which shortly fill the apparatus. In a little time the pe- culiar odor of ozone is evident, and the air of the vessel gives, with iodide-of-potassium-starch-paper, the blue color which indicates ozone. In this experiment ordinary oxy- gen, in the act of uniting with phosphorus, is partially converted into its active modification; and although the larger share of the ozone formed is probably destroyed by uniting with phosphorus, a portion escapes combination and is recognizable in the surrounding air. The ozone thus developed is eis with other bodies, (phcsphorous acid, etc.,) which cause the white cloud. The quantity of ozone that appears in this experiment, : though very small,—under the most favorable circum- stances but *|,,,, of the weight of the air,—is still sufficient to exhibit all the reactions that have been described. Schénbein has shown that various organic bodies which are susceptible of oxidation, viz., citric and tartaric acids, when dissolved in water and agitated with air in the sun- light for half an hour, acquire the reactions of ozone. Ether and alcohol, kept in partially filled bottles, also be- come capable of producing oxidizing effects. Many of the : - a a ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 67 vegetable oils, as oil of turpentine, oil of lemon, oil of cinnamon, linseed oil, etc., possess the property of ozoniz- ing oxygen, or at least acquire oxidizing properties when exposed to the air. Hence the bleaching and corrosion of the cork of a partially filled turpentine bottle. It is a highly probable hypothesis that ozone may be formed in many or even all cases of slow oxidation, and that although the chief part of the ozone thus developed must unite at once with the oxidable substance, a portion of it may diffuse into the atmosphere and escape immediate combination. Ozone is likewise produced in a variety of chemical re- actions, whereby oxygen is liberated from combination at ordinary temperatures. When water is evolved by gal- vanic electricity into free oxygen and free hydrogen, the former is accompanied with a small proportion of ozone. The same is true in the electrolysis of carbonic acid. So, too, when permanganate of potash, binoxide of barium, or chromic acid, is mixed with strong sulphuric acid, ox- ygen gas is disengaged which contains an admixture of ozone.* Is Ozone Produced by Vegetation ?—It is an interesting question whether the oxygen so freely exhaled from the foliage of plants under the influence of sunlight is accom- panied by ozone. Various experimenters have occupied * It appears probable that ozone is developed in all cases of rapid oxidation at high temperatures. This has been long suspected, and Meissner obtained strong indirect evidence of the fact. Since the above was written, Pincus has announ- ced that ozone is produced when hydrogen burns in the air, or in pure oxygen gas. The quantity of ozone thus developed is sufficient to be recognized by the odor. To observe this fact, a jet of hydrogen should issue from a fine orifice and burn with a small flame, not exceeding 34-inch in length. NKO, ~ NEKO, ++). H, 0 Nitrite of Ammonia, NH, NO, is known to the chem- ist as a white crystalline solid, very soluble in water. When its concentrated aqueous solution is gently heated, the salt is gradually resolved into water and nitrogen gas. ~ This decomposition is represented by the following equa- tion: By Oe 2 Oe + | ON This decomposition is, however, not complete. A por- tion of ammonia escapes in the vapors, and nitrous acid accumulates in the residual liquid. (Pettenkofer.) Addi- tion of a strong acid facilitates decomposition; an-alkali retards it. When a dilute solution, 1 : 500, is boiled, but a small portion of the salt is decomposed, and a part of it is found in the distillate. Very dilute solutions, 1 : 100,009, may be boiled without suffering any alteration whatever. (Schéyen.) Schénbein and others have (erroneously ?) supposed that nitrite of ammonia is generated by the direct union of nitrogen and water. Nitrite of ammonia may exist in the atmosphere in minute quantity. Nitrites ef potash and soda may be procured by strongly heating the corresponding nitrates, whereby oxygen gas 1s expelled. The Mutual Convertibility of Nitrates and Nitrites is illustrated by various statements already made. There are, in fact, numerous substances which reduce nitrates to nitrites. According to Schénbein, (Jowr. Prakt. Ch., 84, 207,) this reducing effect is exercised by the albuminoids, by starch, glucose, and milk-sugar, but not by cane-sugar. t V4 HOW CROPS FEED. ae eae It is also manifested by many metals, as zine, iron, and — lead, and by any mixture evolving hydrogen, as, for ex- ample, putrefying organic matter. On the other hand, ozone instantly oxidizes nitrites to nitrates. Reduction of Nitrates and Nitrites te Ammonia. — Some of the substances which convert nitrates into nitrites: may also by their prolonged action transform the latter into ammonia. When small fragments of zinc and iron mixed together are drenched with warm solution of caustic potash, hydrogen is copiously disengaged. Ifa nitrate be added to the mixture, it is at once reduce d, and ammonia escapes. If to a mixture of zinc or iron AE dilute chlor- hydric acid, such as is employed in preparing hydrogen gas, nitric acid, or any nitrate or nitrite be added, the evolution of hydrogen ceases, or is checked, and ammonia is formed in the solution, whence it can be expelled by lime or potash. Nitric acid. Hydrogen. Ammonia, Water. NOB: +: 8H =i NH). ee The appearance of nitrous acid in this process is an in- termediate step of the reduction. Further Reduction of Nitric and Nitrous Acids.—Un- der certain conditions nitric acid and nitrous acid are still further deoxidized. Nesbit, who first employed the reduc- tion of nitric acid to ammonia by means of zine and dilute chlorhydric acid as a means of determining the quantity of the former, mentions (Quart. Jour. Chem. Soc., 1847, p: 283,) that when the temperature of the liquid is allowed to rise somewhat, nitric oxide gas, NO, escapes. From weak nitric acid, zinc causes the evolution of ni- trous oxide gas, N,O. | As already mentioned, nitrate of ammonia, when heated to fusion, evolves nitrous oxide, N,O. Emmet showed that by immersing a strip of zine in the melted salt, nearly pure nitrogen gas is set free. ee Pe ae ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 15 When nitric acid is heated with lean flesh (fibrin), nitric - oxide and nitrogen gases both appear. It is thus seen that by successive steps of deoxidation nitric acid may _ be gradually reduced to nitrous acid, ammonia, nitric oxide, ' nitrous oxide, and finally to nitrogen. Wests for Nitric and Nitroms Acids. — The fact that these substances often occur in extremely minute quantities renders it needful to employ very delicate tests for their recognition. Price’s Test.—F ree nitrous acid decomposes iodide.of potassium in the same manner as ozone, and hence gives a blue color, with a mixture of this salt and starch-paste. Any nitrite produces the same effect if to the mixture dilute sulphuric acid be added to liberate the nitrous acid. Pure nitric acid, if moderately dilute, and dilute solutions of nitrates mixed with dilute sulphuric acid, are without immediate effect upon iodide-of-potassium-starch-paste. If the solution of a nitrate be min- gled with dilute sulphuric acid, and agitated for some time with zine filings, reduction to nitrite occurs, and then addition of the starch-paste, ete., gives the blue coloration. According to Schénbein, this test, first proposed by Price, will detect nitrous acid when mixed with one-hund- red-thousand times its weight of water. It is of course only applicable in the absence of other oxidizing agents. Green Vitriol Test.—A very characteristic test for nitric and nitrous acids, and a delicate one, though less sensitive than that just describ- ed, is furnished by common green vitriol, or protosulphate of iron. Nitric oxide, the red gas which is evolved from nitric acid or nitrates by mixing them with excess of strong sulphuric acid, and from nitrous acid or nitrites by addition of dilute sulphuric acid, gives with green vitriol a peculiar blackish-brown coloration. To test for minute quantities of nitrous acid, mix the solution with dilute sulphuric acid and cautiously pour this liquid upon an equal bulk of cold saturated solution of green vitriol, so that the former liquid floats upon the latter without mingling much with it. On standing, the coloration will be perceived where the two liquids are in contact. Nitric acid is tested as follows: Mix the solution of nitrate with an equal yolume of concentrated sulphuric acid; let the mixture cool, and pour upon it the solution of green vitriol. The coloration will appear between the two liquids. Formation of Nitrogen Compounds in the Atmosphere. —a. From free nitrogen, by electrical ozone. Schdénbein and Meissner have demonstrated that a discharge of elec- tricity through air in its ordinary state of dryness causes oxygen and nitrogen to unite, with the formation of nitric peroxide, NO,. Meissner has proved that not the elec- 76 HOW CROPS FEED. : | tricity directly, but the ozone developed by it, accom-— plishes this oxidation. It has long been known that nitric — trous acids thus: 2NO, + H,O = NO. . +N « « peroxide decomposes with water, yielding nitric and ni-— { It is further known that nitrous acid, both in the free — state and in combination, is instantly oxidized to nitric acid by contact with ozone. — Thus is explained the ancient observation, first made by Cavendish in 1784, that when electrical sparks are trans- mitted through moist air, confined over solution of potash, nitrate of potash is formed. (For information regarding this salt, see p. 252.) Until recently, it has been supposed that nitric acid is present in only those rains which accompany thunder- storms. It appears, however, from the analyses of both Way and Boussingault, that visible or audible electric discharges do not perceptibly influence the proportion of nitric acid in the air; the rains accompanying thunder-storms not being always nor usually richer in this substance than others. Von Babo and Meissner have demonstrated that silent electrical discharges develop more ozone than flashes of lightning. Meissner has shown that the electric spark causes the copious formation of nitric peroxide in its im- mediate path by virtue of the heat it excites, which in- creases the energy of the ozone simultaneously produced, and causes it to expend itself at once in the oxidation of — nitrogen. Boussingault informs us that in some of the tropical regions of South America audible electrical dis- charges are continually taking place throughout the whole year. In our latitudes electrical disturbance is perpetu- ally occurring, but equalizes itself mostly by silent dis- charge. The ozone thus noiselessly developed, though operating at a lower temperature, and therefore more ATMOSPHERIC AIR AS THE FOOD OF PLANTS. oer § slowly than that which is produced by lightning, must really oxidize much more nitrogen to nitric acid than the latter, because its action never ceases. Formation of Nitrogen Compounds in the Atmosphere. —b. From free nitrogen (by ozone?) in the processes of combustion and slow oxidation. At high temperatures.—Saussure first observed (Ann. de Chimie, 1xxi, 282), that in the burning of a mixture of oxygen and hydrogen gases in the air, the resulting water contains ammonia. THe had previously noticed that nitric acid and nitrous acid are formed in the same process. Kolbe (Ann. Chem. u. Pharm., cxix, 176) found that when a jet of burning hydrogen was passed into the neck of an open bottle containing oxygen, reddish-yellow va- pors of nitrous acid or nitric peroxide were copiously pro- duced on atmospheric air becoming mingled with the burning gases. Bence Jones (Phil. Trans., 1851, ii, 899) discovered ni- tric (nitrous?) acid in the water resulting from the burn- ing of alcohol, hydrogen, coal, wax, and purified coal-gas. By the use of the iodide-ofpotassium-starch test (Price’s test), Boettger (Jour. fiir Prakt. Chem., \xxxv, 396) and Schénbein (ibid., lxxxiv, 215) have more recently confirm- ed the result of Jones, but because they could detect neither free acid nor free alkali by the ordinary test-pa- pers, they concluded that nitrous acid and ammonia are simultaneously formed, that, in fact, nitrite of ammonia is generated in all cases of rapid combustion. Meissner ( Untersuchungen iiber den Sauerstoff, 1863, p. 283) was unable to satisfy himself that either nitrous acid or ammonia is generated in combustion. Finally, Zabelin (Ann. Chem. u. Ph., cxxx, 54) in a series of careful experiments, found that when alcohol, il- luminating gas, and hydrogen, burn in the air, nitrous acid and ammonia are very frequently, but not always, formed. 78 HOW CROPS FEED. When the combustion is so perfect that the resulting wa- ter is colorless and pure, only nitrous acid is formed ; when, on the other hand, a trace of organic matters es- — capes oxidation, less or no nitrous acid, but in its place ammonia, appears in the water, and this under circum- stances that preclude its absorption from the atmosphere. Zabelin gives no proof that the combustibles he em- ployed were absolutely free from compounds of nitrogen, but otherwise, his experiments are not open to criticism. Meissner’s observations were indeed made under some- what different conditions; but his negative results were not improbably arrived at simply because he employed a much less delicate test for nitrous acid than was used by Schonbein, Boettger, Jones, and Zabelin.* We must conclude, then, that nitrous acid and ammonia are usually formed from atmospheric nitrogen during rap- id combustion of hydrogen and compounds of hydrogen and carbon. The quantity of these bodies thus generated is, however, in general so extremely small as to require the most sensitive reagents for their detection. At low temperatures.—Schonbein was the first to observe that nitric acid may be formed at moderately elevated or even ordinary temperatures. He obtained several grams of nitrate of potash by adding carbonate of potash to the liquid resulting from the slow oxidation of sae in the preparation of ozone. More recently he believed to have discovered that ni- trogen compounds are formed by the simple evaporation of water. He heated a vessel (which was indifferently of * Meissner rejected Price’s test in the belief that it cannot serve to distinguish nitrous acid from peroxide of hydrogen, He Oz. He therefore made the liquid to be examined alkaline with a slight excess of potash, concentrated to small bulk and tested with dilute sulphuric acid and protosulphate of iron. (Unters. ii, A. Sauerstoff, p, 233), Schénbein had found that iodide of potassium is decom- posed after a little time by concentrated solutions of peroxide of hydrogen, but is unaffected by this body when dilute, (Jour. fiir prakt. Chem., \xxxvi, p. 90). Zabelin agrees with Schénbein that Price’s test is decisive between peroxide of hydrogen and nitrous acid. (Ann, Chem, u. Ph., CXXX, p. 58.) me ee ae eee ee ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 79 glass, porcelain, silver, etc.,) so that water would evapo- rate rapidly from its surface. The purest water was then dropped into the warm dish in small quantities at a time, each portion being allowed to evaporate away before the next was added. Over the vapor thus generated was held the mouth of a cold bottle until a portion of the vapor was condensed in the latter. The water thus collected gave the reactions for nitrous acid and ammonia, sometimes quite intensely, again faint- ly, and sometimes not at all. By simply exposing a piece of filter-paper for a suffi- cient time to the vapors arising from pure water heated to boiling, and pouring a few drops of acidified iodide-of- potassium-starch-paste upon it, the reaction of nitrous acid was obtained. When paper which had been impregnated with dilute solution of pure potash was hung in the va- pors that arose from water heated in an open dish to 100° F’., it shortly acquired so much nitrite of potash as to re- act with the above named test. Lastly, nitrous acid and ammonia appeared when a sheet of filter-paper, or a piece of linen cloth, which had been moistened with the purest water, was allowed to dry at ordinary temperatures, in the open air or in a closed vessel. (Jour. fiir Prakt. Chem., \xvi, 131.) These ex- periments of Schénbein are open to criticism, and do not furnish perfectly satisfactory evidence that nitrous acid and ammonia are generated under the circumstances men- tioned. Bohlig has objected that these bodies might be gathered from the atmosphere, where they certainly exist, though in extremely minute quantity. Zabelin, in the paper before referred to (Ann. Ch. Ph., Cxxx, p. 76), communicates some experimental results which, in the writer’s opinion, serve to clear up the mat- ter satisfactorily. Zabelin ascertained in the first place that the atmos- pheric air contained too little ammonia to influence Ness- 80 HOW CROPS FEED. ler’s test,* which is of extreme delicacy, and which he con- stantly employed in his investigations. Zabelin operated in closed vessels. The apparatus he used consisted of two glass flasks, a larger and a smaller . one, which were closed by corks and fitted with glass tubes, so that a stream of air entering the larger vessel should bubble through water covering its bottom, and thence passing into the smaller flask should stream through Nessler’s test. Next, he found that no ammonia and (by Price’s test) but doubtful traces of nitrous acid could be detected in the purest water when distilled alone in this apparatus. Zabelin likewise showed that cellulose (clippings of filter- paper or shreds of linen) yielded no ammonia to Nessler’s test when heated in a current of air at temperatures of 120° to 160° F. Lastly, he found that when cellulose and pure water to- gether were exposed to a current of air at the tempera- tures just named, ammonia was at once indicated by Nessler’s test. Nitrous acid, however, could be detected, if at all, in the minutest traces only. Views of Schinbein.—The reader should observe that Boettger and Schénbein, finding in the first instance by the exceedingly sensitive test with iodide of potassium and starch-paste, that nitrous acid was formed, when hy- drogen burned in the air, while the water thus generated was neutral in its reaction with the vastly less sensitive litmus test-paper, concluded that the nitrous acid was united with some base in the form of a neutral salt. Af- terward, the detection of ammonia appeared to demon- strate the formation of nitrite of ammonia. We have already seen that nitrite of ammonia, by ex- posure to a moderate heat, is resolved into nitrogen and water. Schénbein assumed that under the conditions of * See p. 54. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 81 his experiments nitrogen and water combine to form ni- trite of ammonia. BN 2) H.0- =" NE NO This theory, supported by the authority of so distin- guished a philosopher, has been almost universally credit- ed.* It has, however, little to warrant it, even in the way of probability. If traces of nitrite of ammonia can be produced by the immediate combination of these excep- tionally abundant and universally diffused bodies at com- mon temperatures, or at the boiling point of water, or lastly in close proximity to the flames of burning gases, then it is simply inconceivable that a good share of the atmosphere should not speedily dissolve in the ocean, for the conditions of Schénbein’s experiments prevail at all times and at all places, so far as these substances are con- cerned. The discovery of Zabelin that ammonia and nitrous acid do not always appear in equivalent quantities or even simultaneously, while difficult to reconcile with Schén- bein’s theory, in no wise conflicts with any of his facts. A quantity of free nitrous acid that admits of recognition by help of Price’s test would not necessarily have any effect on litmus or other test for free acids. There re- mains, then, no necessity of assuming the generation of ni- trite of ammonia, and the fact of the separate appearance of the elements of this salt demands another explanation. The Author's Opinion.—The writer is not able, perhaps, to offer a fully satisfactory explanation of the facts above adduced. He submits, however, some speculations which appear to him entirely warranted by the present aspects of the case, in the hope that some one with the time at * Zabelin was inclined to believe that his failure to detect nitrous acid in some of his experiments where organic matters intervened, was due to a power pos- sessed by these organic matters to mask or impair the delicacy of Price’s test, as first noticed by Pettenkofer and since demonstrated by Schonbein in case of urine. 4% 82 HOW CROPS FEED. command for experimental study, will establish or disprove them by suitable investigations. He believes, from the existing evidence, that free nitro- gen can, in no case, unite directly with water, but in the conditions of all the foregoing experiments, it enters com- bination by the action of ozone, as Schénbein formerly maintained and was the first to suggest. We have already recounted the evidence that goes to show the formation of ozone in all cases of oxidation, both’ at high and low temperatures, p. 67. In Zabelin’s experiments we may suppose that ozone was formed by the oxidation of the cellulose (linen and paper) he employed. In Schénbein’s experiments, where paper or linen was not employed, the dust of the air may have supplied the organic matters. The first result of the oxidation of nitrogen is nitrous acid alone (at least Schénbein and Bohlig detected no ni- tric acid), when the combustion is complete, as in case of hydrogen, or when organic matters are excluded from the experiment. Nitric acid is a product of the subsequent. oxidation of nitrous acid. When organic matters exist in the product of combustion, as when alcohol burns in a heated apparatus yielding water having a yellowish color, it is probable that nitrous acid is formed, but is afterward reduced to ammonia, as has been already explained, p. 74. Zabelin, in the article before cited, refers to Schénbein as authority for the fact that various organic bodies, viz., all the vegetable and animal albuminoids, gelatine, and most of the carbohydrates, especially starch, glucose, and milk-sugar, reduce nitrites to ammonia, and ultimately to nitrogen; and although we have not been able to find such a statement in those of Schénbein’s papers to which we have had access, it is entirely credible and in accordance with numerous HEN eo If, as thus appears extremely probable, ozone is devel- oped in all cases of oxidation, both rapid and slow, then ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 83 every flame and fire, every decaying plant and animal, the organic matters that exhale from the skin and lungs of living animals, or from the foliage and flowers of plants, especially, perhaps, the volatile oils of cone-bearing trees, are, indirectly, means of converting a portion of free ni- trogen into nitrous and nitric acids, or ammonia. These topics will be recurred to in our discussion of Nitrification in the Soil, p. 254. Formation of Nitrogen Compounds in the Atmosphere. —c. From free nitrogen by ozone accompanying the oxy- gen exhaled from green foliage in sunlight. The evidence upon the question of the emission of ozone by plants, or of its formation in the vicinity of foliage, has been briefly presented on page 68, The present state of investigation does not permit us to pronounce definitely upon this point. There are, however, some facts of agri- culture which, perhaps, find their best explanation by as- suming this evolution of ozone. It has long been known that certain crops are especially aided in their growth by nitrogenous fertilizers, while oth- ers are comparatively indifferent to them. Thus the cereal grains and grasses are most frequently benefited by appli- cations of nitrate of soda, Peruvian guano, dung of ani- mals, fish, flesh and blood manures, or other matters rich in nitrogen. On the other hand, clover and turnips flour- ish best, as a rule, when treated with phosphates and alka- line substances, and are not manured with animal fertiliz- ers so economically as the cereals. It has, in fact, become a rule of practice in some of the best farming districts of England, where systematic rotation of crops is followed, to apply nitrogenous manures to the cereals and phos- phates to turnips. Again, it is a fact, that whereas nitro- genous manures are often necessary to produce a good wheat crop, in which, at 30 bu. of grain and 2,600 Ibs. of straw, there is contained 45 lbs. of nitrogen; a crop of clover may be produced without nitrogenous manure, in 84 HOW CROPS FEED. which would be taken from the field twice or thrice the above amount of nitrogen, although the period of growth of the two crops is about the same. Ulbricht found in his investigation of the clover plant (Vs. S¢., IV., p. 27) that the soil appears to have but little imfluence on the content of nitrogen of clover, or of its individual organs. These facts admit of another expression, viz.: Clover, though containing two or three times more nitrogen, and requiring correspondingly larger supplies of nitrates and ammonia than wheat, 7s able to supply itself much more easily than the latter crop. In parts of the Genesee wheat region, it is the custom to alternate clover with wheat, be- cause the decay of the clover stubble and roots admirably prepares the ground for the last-named crop. The same preparation might be had by the more expensive process of dressing with a highly nitrogenous manure, and it is scarcely to be doubted that it is the nitrogen gathered by the clover which insures the wheat crop that follows. It thus appears that the plant itself causes the formation in its neighborhood of assimilable compounds of nitrogen, and that some plants excel others in their power of accom- plishing this important result. On the supposition that ozone is emitted by plants, it is plain that those crops which produce the largest mass of foliage develop it most abundantly. By the action of this ozone, the nitrogen that bathes the leaves is convert- ed into nitric acid, which, in its turn, is absorbed by the plant. The foliage of clover, cut green, and of root crops, maintains its activity until the time the crop is gathered ; the supply of nitrates thus keeps pace with the wants of the plant. In case of grain crops, the functions of the fo- liage decline as the seed begins to develop, and the plant’s means of providing itself with assimilable nitrogen fail, although the need for it still exists. Furthermore, the clover cut for hay, leaves behind much more roots and stubble per acre than grain crops, and the clover stubble ee ee ee ee ee ee, ethene 8 ATMOSPHERIC AIR AS THE FOOD OF PLANTS, 85 is twice as rich in nitrogen as the stubble of ripened grain. This is a result of the fact that the clover is cut when in active growth, while the grain is harvested after the roots, stems, and leaves, have been exhausted of their own juices to meet the demands of the seed. ~~ ‘Whatever may be the value of our explanations, the fact is not to be denied that the soil is enriched in nitrogen by the culture of large-leaved plants, which are harvested while in active growth, and leave 4 considerable propor- tion of roots, leaves, or stubble, on the field. On the other hand, the field is impoverished in nitrogen when grain crops are raised upon it. Formation of Nitric Acid from Ammonia.—Ammonia (carbonate of ammonia) under the influence of ozone is converted into nitrate of ammonia, (Baumert, Houzeau). The reaction is such that one-half of the ammonia is oxid- ized to nitric acid, which unites with the residue and with water, as illustrated by the equation: Ne 4 Oo NE NO} ot HO In this manner, nitrate of ammonia may originate in the atmosphere, since, as already shown, ammonia and ozone are both present there. Oxidation and Reduction in the Atmosphere, — The fact that ammonia and organic matters on the one hand, and ozone, nitrous and nitric acids on the other, are pres- ent, and, perhaps, constantly present in the air, involves at first thought a contradiction, for these two classes of sub- stances are in a sense incompatible with each other. Organic matters, ammonia, and nitrous acid, are converted by ozone into nitric acid. On the contrary, certain or- ganic matters reduce ozone to ordinary oxygen, or destroy it altogether, and reduce nitric and nitrous acids to am- monia, or, perhaps, to free nitrogen. The truth is that the substances named. are being perpetually composed and decomposed in the atmosphere, and at the surface of the 86 HOW CROPS FEED, soil, Here, or at one moment, oxidation prevails; there, or at another moment, reduction preponderates. It is only as one or another of the results of this incessant ac- tion is withdrawn from the sphere of change, that we can give it permanence and identify it, The quantities we measure are but resultants of forces that oppose each oth- er. The idea of rest or permanence is as foreign to the chemistry of the atmosphere as to its visible phenomena. Nitric Acid in the Atmosphere.—The occurrence of ni- tric acid or nitrate of ammonia in the atmosphere has been abundantly demonstrated in late years (1854-6) by Cloez, Boussingault, De Luca, and Kletzinsky, who found that when large volumes of air are made to bubble through solutions of potash, or to stream over fragments of brick or pumice which have been soaked in potash or carbonate of potash, these absorbents gradually acquire a small amount of nitric acid, In the experiments of Cloez and De Luca, the air was first washed of its ammonia by con- tact with sulphuric acid. Their results prove, therefore, that the nitric acid was formed independently of ammonia, though it doubtless exists in the air in combination with this base. Proportion of Nitric Acid in Rain-water, etc.—In at- mospheric waters, nitric acid is found much more abund- antly than in the air itself, for the reason that a small bulk of rain, etc., washes an immense volume of air. Many observers, among the first, Liebig, have found ni- trates in rain-water, especially in the rain of thunder- storms. The investigations of Boussingault, made in 1856-8, have amply confirmed Barral’s observation that nitric acid (in combination) is almost invariably present in rain, dew, fog, hail, and snow. Boussingault, (Agronomie, etc., IL, 325) determined the quantity of nitric acid in 184 rains, 31 snows, 8 dews, and 7 fogs. In only 16 instances out of these 180 was the amount of nitric acid too small ee ee ee Oe ee ll i es ee nls ee ee a ee ; . ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 87 to detect. The greatest proportion of nitric acid found in rain occurred in a slow-falling morning shower, (9th Octo- ber, 1857, at Liebfrauenberg), viz., 62 parts * in 10 million of water. In fog, on one occasion, (at Paris, 19th Dec., 1857,) 101 parts to 10 million of water were observed. Knop found in rain-water, collected near Leipzig, in July, 1862, 56 parts; in rain that fell during a thunder- storm, 98 parts in 10 million of water. Boussingault found in rain an average of 2 parts, in snow of 4 parts, of nitric acid to 10 million of water. Mr. Way, whose determinations of ammonia in the at- mospheric waters collected by Lawes and Gilbert, at Rothamstead, during the whole of the years 1855-6, have already been noticed, (p. 63,) likewise estimated the nitric -acid in the same waters. He found the proportion of ni- tric acid to be, in 1855, 4 parts, in 1856 44 parts, to 10 million of water. Bretschneider found at Ida-Marienhiitte, Prussia, for the . year 1865-6 an average of 83 parts, for 1866-7 an average of 44 parts, of nitric acid in 10 million of water. At Regen- walde, Prussia, the average in 1865-6 was 25 parts, in 1866-7, 22 parts. At Proskau, the average in 1864-5 was 31 parts. At Kuschen, the average for 1864-5 was 6 parts; in 1865-6, 7; in 1866-7, 8 parts. At Dahme, in 1865-6, the average was 12 parts. At Insterburg, Pincus and Rollig obtained in 1864-5, an average of 12 parts; in 1865-6, an average of 16 parts of nitric acid in 10 million of water. The highest monthly average was 280 parts, at Lauersfort, July, 1864; and the lowest was nothing, April, 1865, at Ida-Marienhiitte. Quantity ef Nitric Acid in Atmospheric Water.—The total quantity of nitric acid that could be collected in the rains, etc., at Rothamstead, amounted in 1855 to 2.98 lbs., and in 1856 to 2.80 lbs. per acre. * Tn all the quantitative statements here and elsewhere, anhydrous nitric acid, Ne O;, (O=16, formerly NO5, O=S8) is to be understood. 88 HOW CROPS FEED. This quantity was very irregularly distributed among the months. In 1855 the smallest amount was collected in January, the largest in October, the latter being nearly 20 times as much as the former. In 1856 the largest quantity occurred in May, and the smallest in February, - the former not quite six times as much as the latter. The following table gives the results of Mr. Way entire. (Jour. Roy. Ag. Soc. of Eng., XVU, pp. 144 and 620.) Amounts oF RAIN AND OF AmmMontié, Nitric AcID, AND TOTAL NITROGEN therein, collected at Rothamstead, Eng., in the years 1855-6—calculated per acre, according to Messrs. Lawes, Gilbert, and Way. Quantity of Rain| smmonia| Nitric | Total Né- in Imperial Gal- fh acid in \trogen in phe he fees 10) grains. | grains. | grains. 1855 1856 1855) 1856 |1855)1856/ 1855) 1856 RATIIEN: eer iere ue sitare ats e 13.523) 62.952/1244) 5005 | 280)1561)1084) 4526. INGDRUAT Yate eo ks ee oe toe oie 22.473) 30.586)2337| 4175 | 944) 544/2169) 3579 VIS nee eon ca ito ste siseaie ato creo ** Soda, 8.948 77 ‘* Protoxide of iron, .879 Silica, 1.283 Phosphate of lime, trace Solid matters, Carbonic acid gas, (407.647 cubic inches at 52° Fah.) Water, 552.799 58,317,110 grains. 4c ss The waters of ordinary springs and rivers, as well as those that fall upon the earth’s surface as rain, are, indeed, * The Saxon pound contains 7,680 Saxon grains. 6* \ 130 HOW CROPS FEED. by no means fully charged with carbonic acid, and their solvent effect is much less than that exerted by water sat- urated with this gas. The quantity (by volume) of carbonic acid in 10,000 parts of rain-water has been observed as follows: Accord- ing to Locality. Lampadius, 8 Country near Freiberg, Saxony. Mulder, 20 City of Utrecht, Holland. Von Baumhauer, 40 to 90 iad od fs Peligot, 5 ? The quantities found are variable, as might be expected, and we notice that the largest proportion above cited does not even amount to one per cent. _ Inriver and spring water the quantities are somewhat larger, but the carbonic acid exists chiefly in chemical com- bination as bicarbonates of lime, magnesia, ete. In the capillary water of soils containing much organic matters, more carbonic acid is dissolved. According to a single observation of De Saussure’s, such water contains 2°|, of the gas. In a subsequent paragraph, p. 221, is given the reason of the small content of carbonic acid in these waters. The weaker action of these dilute solutions, when con- tinued through long periods of time and extending over an immense surface, nevertheless accomplishes results of vast significance. Solutions of Alkali-Salts.—Rain-water, as we have already seen, contains a minute quantity of salts of am- monia (nitrate and bicarbonate). The water of springs and rivers acquires from the rocks and soil, salts of soda and potash, of lime and magnesia. These solutions, dilute though they are, greatly surpass pure water, or even car- bonated water, in their solvent and disintegrating action. Phosphate of lime, the earth of bones, is dissolved by pure water to an extent that is hardly appreciable; in ORIGIN AND FORMATION OF SOILS. 131 salts of ammonia and of soda, however, it is taken up in considerable quantity. Solution of nitrate of ammonia dissolves lime and magnesia and their carbonates with great ease. In general, up to a certain limit, a saline so- lution acquires increased solyent power by increase in the amount and number of dissolved matters. This import- ant fact is one to which we shall recur at another time. Action of Oxygen.—This element, the great mover of chemical changes, which is present so largely in the at- mosphere, has a strong tendency to unite with certain bodies which are almost universally distributed in the rocks. On turning to the analyses of minerals, p. 110, we notice in nearly every instance a quantity of protoxide of iron, or protoxide of manganese. The green, dark gray, or black minerals, as the micas, amphibole, pyroxene, chlorite, talc, and serpentine, invariably contain these prot- oxides in notable proportion. -In the feldspars they exist, _indéed, in very minute quantity, but are almost never en- tirely wanting. Sulphide of iron (iron pyrites), in many of its forms, is also disposed to oxidize its sulphur to sul- phurie acid, its iron to sesquioxide, and this mineral is widely distributed as an admixture in many rocks. In trap or basaltic rocks, as at Bergen Hill, metallic iron is said to occur in minute proportion,* and in a state of fine division. The oxidation of these substances materially hastens the disintegration of the rocks containing them, since the higher oxides of iron and of manganese occupy more space than the metals or lower oxides. This fact is well illustrated by the sulphate of protoxide of iron (cop- peras, or green-vitriol), which, on long keeping, exposed to the air, is converted from transparent, glassy, green crys- tals to a bulky, brown, opaque powder of sulphate of sesquioxide of iron. Weathering.—The conjoined influence of water, car- * This statement rests on the authority of Professor Henry Wurtz, of New York. 132 HOW CROPS FEED. bonic acid, oxygen, and the salts held in solution by the - atmospheric waters, is expressed by the word weathering. This term may likewise include the action of frost. When rocks weather, they are decomposed or dissolved, and new compounds, or new forms of the original mat- ter, result. The soil is a mixture of broken or pulverized rocks, with the products of their alteration by weathering. a. Weathering of Quartz Rock.—Quartz (silicic acid), as occurring nearly pure in quartzite, and in many sand- stones, or as a chief ingredient of all the granitic, horn- blendic, and many other rocks, is so exceedingly hard and insoluble, that the lifetime of a man is not sufficient for the direct observation of any change in it, when it is ex- posed to ordinary weathering. It is, in fact, the least destructible of the mineral elements of the globe. Never- theless, quartz, even when pure, is not absolutely insoluble, particularly in water containing alkali carbonates or sili- cates. In its less pure varieties, and especially when as- sociated with readily decomposable minerals, it is acted on more rapidly. The quartz of granitic rocks is usually roughened on the surface when it has long been exposed to the weather. 6. The Feldspars weather much more easily than quartz, though there are great differences among them. The soda and lime feldspars decompose most readily, while the potash feldspars are often exceedingly durable. The decomposition results in completely breaking up the hard, glassy mineral. In its place there remains a white or yellowish mass, which is so soft as to admit of crush- ing between the fingers, and which, though usually, to the naked eye, opaque, and non-crystalline, is often seen, under a powerful magnifier, to contain numerous transparent crys- talline plates. The mass consists principally of the crys- talline mineral, kaolinite, a hydrated silicate of alumina, (the analysis of which has been given already, p. 113,) mixed ORIGIN AND FORMATION OF SOILS. 133 with hydrated silica, and often with grains of undecompos- ed mineral. If we compare the composition of pure pot- ash feldspar with that of kaolinite, assuming, what is probably true, that all the alumina of the former remains in the latter, we find what portions of the feldspar have been removed and washed away by the water, which, to- gether with carbonic acid, is the agent of this change. Feldspar. Kaolinite. Liberated. Added. Pm. 2... . 18.3 18.3 0 PMN Pefea.s Meet as os 1865, 39 48 74 16 10 — s “ ** precipitated, 1864, 65 _ 81 19 0 — - Separhe - 1865, 51 52 q7 15 8 —_ Carbonate of magnesia, 729 125 64 q 29 — Gypsum, pulverized, 17 = 81 19 0 aa From these figures we gather: 1. The gaseous mixture which is contained in the pores of solid substances rarely has the composition of the at- mosphere. In but two instances, viz., with gypsum and precipitated carbonate of lime, were only oxygen and ni- trogen absorbed in proportions closely approaching those of the atmosphere. 2. Nitrogen appears to be nearly always absorbed in greater proportion than oxygen, and is greatly condensed in some cases, as by peat, hydrated oxide of iron, and car- bonate of magnesia. 168 HOW CROPS FEED. 8. Oxygen is often nearly or quite wanting, as in char. — coal, oxide of iron, alumina, river silt, and whiting. —a 4, Carbonic acid, though sometimes wanting entirely, — is usually abundant in the absorbed gases. 5. In the pores of charcoal and of soils containing de- caying organic matters, carbonic acid is often partially re- placed by carbonic oxide. The experiments, however, do not furnish proof that this substance is not formed under the influence of the high temperature employed (284° F.) in expelling the gases, rather than by incomplete oxidation of organic matters at ordinary temperatures. 6. A substance, when moist, absorbs less gas than when dry. Inaccordance with this observation, De Saussure no- ticed that dry charcoal saturated with various gases evolv- ed a good share of them when moistened with water. Ground (and burnt?) coffee, as Babinet has lately stated, evolves so much gas when drenched with water as to burst a bottle in which it is confined. The extremely variable figures obtained by Blumtritt when operating with the same substance (the figures given in the table are averages of two or three usually discordant results), result from the general fact that the proportion in which a number of gases are present in a mixture, in- fluences the proportion of the individual gases absorbed. Thus while charcoal or soil will absorb a large amount of ammonia from the pure gas, it will take up but traces of this substance from the atmosphere of which ammonia is but an infinitesimal ingredient. ; So, too, charcoal or ‘soil saturated with ammonia by ex- posure to the unmixed gas, loses nearly all of it by stand- ing in the air for some time. This is due to the fact that gases attract each other, and the composition of the gas condensed in a porous body varies perpetually with the variations of composition in the surrounding atmosphere. It is especially the water-gas (vapor of water) which is a fluctuating ingredient of the atmosphere, and one which c i i Tair it i PHYSICAL CHARACTERS OF THE SOIL. 169 is absorbed by porous bodies in the largest quantity. This not only displaces other gases from their adhesion to solid surfaces, but by its own attractions modifies these adhesions. Reichardt and Blumtritt take no account of water-gas, except in the few experiments where the substances were purposely moistened. In all their trials, however, moist- ure was present, and had its quantity been estimated, doubtless its influence on the extent and kind of absorp- tion would have been strikingly evident throughout. Ammonia and carbonate of ammonia in the gaseous form are absorbed from the air by the dry soil, to a less degree than by a soil that is moist, as will be noticed fully hereafter. — Chemical Action induced by Adhesion.—This physical property often leads to remarkable chemical effects; in other words, adhesion exalts or brings into play the force of affinity. When charcoal absorbs those emanations from putrefying animal matters which we scarcely know, save by their intolerable odor and poisonous influence, it causes at the same time their rapid and complete oxida- tion; and hence a piece of tainted meat is sweetened by covering it with a thin layer of powdered charcoal. As Stenhouse has shown, the carcass of a small animal may be kept in a living-room during the hottest weather with- out giving off any putrid odor, provided it be surrounded on all sides by a layer of powdered charcoal an inch or more thick, Thus circumstanced, it simply smells of am- monia, and its destructible parts are resolved directly in- to water, carbonic acid, free nitrogen, and ammonia, pre- cisely as if they were burned in a furnace, and without the appearance of any of the effluvium that ordinarily arises from decaying flesh. | The metal platinum exhibits a remarkable condensing power, which is manifest even with the polished surface of foil or wire; but is most striking when the metal is 8 170 HOW CROPS FEED. brought to the condition of sponge, a form it assumes when certain of its compounds (e. g. ammonia-chloride of platinum) are decomposed by heat, or to the more finely divided state of platinum black. The latter is capable of condensing from 100 to 250 times its volume’ of oxygen, according to its mode of preparation (its porosity ?); and for this reason it possesses intense oxidizing power, so that, for example, when it is brought into a mixture of oxygen and hydrogen, it causes them to unite explosively. oo e ose eee Lise gleteie es 51 45.7 Plone h Aang soins sb, s ines eee et eee 52 32.0 Heavy clay, (eighty per cent clay, )oisiss.2. 6c... 61 34.9 Pure Oray: Clvy.JA>. os <2 a5 se Ree eee eee meee 70 31.9 Fine carbonate of. limes; eileen hotest aie sk 85 . 28.0 Garden mold: : Js. ghoscee amie eee he siete as 89 24.3 EPO MNBA So oils old boc LR ee eee ee ee Bipleee wee ae sheds 181 25.5 Fine carbonate of maonesing es. 626s send ae oie ae 256 10.8 It is obvious that these two columns express nearly the same thing in different ways. The amount of water re-— rr PERMEABILITY OF SOILS TO LIQUID WATER. 181 tained increases from quartz sand to magnesia. The rap- idity of drying in the air diminishes in the same direction. Some observations of Zenger ( Wilda’s Centralblatt, 1858, 1, 430) indicate the influence of the state of division of a soil on its power of imbibing water. In the subjoin- ed table are given in the first column the per cent of wa- ter imbibed by various soils which had been brought to nearly the same degree of moderate fineness by sifting off both the coarse and the fine matter; and the second col- umn gives the amounts imbibed by the same soils, reduced to a high state of division by pulverization. Coarse. Fine. Quartz sand, 26.0 53.5 Marl (used as fertilizer, ) 30.2 54.5 Marl, underlying peat, 39.0 48.5 Brick clay, 66.2 57.5 Moor soil, 104.5 101.0 Alm (lime-sinter, ) 108.3 70.4 Alm soil, 178.2 102.5 Peat dust, 377.0 268.5 The effects of pulverization on soils whose particles are compact is to increase the surface, and increase to a cor- responding degree the imbibing power. On soils consist- ing of porous particles, lixe lime-sinter and peat, pulver- ization destroys the porosity to some extent and diminishes the amount of absorption. The first class of soils are probably increased in bulk, the latter reduced, by grinding. Wilhelm, ( Wilda’s Centralblatt, 1866, 1, 118), in a series of experiments on. various soils, confirms the above results of Zenger. He found, e. g., that a garden mould imbibed 114 per cent, but when pulverized absorbed but 62 per cent. To illustrate the different properties of various soils for which the farmer has but one name, the fact may be ad- duced that while Schiibler, Zenger, and Wilhelm found the imbibing power of “clay” to range between 40 and 70 per cent, Stoeckhardt examined a “clay” from Saxony 182 HOW CROPS FEED that held 150 per cent of water. So the humus of Schiib- ler imbibed 181 per cent; the peat of Zenger, 377 per cent; _ while Wilhelm examined a very porous peat that took up 519 per cent. These differences are dependent mainly on the mechanical texture or porosity of the material. The want of capillary retentive power for*water in the case of coarse sand is undeniably one of the chief reasons of its unfruitfulness. The best soils possess a medium re- tentive power. In them, therefore, are best united the conditions for the regular distribution of the soil-water under all circumstances. In them this process is not hin- dered too much either by wet or dry weather. The re- taining power of humus is seen to be more than double that of clay. This result might appear at first sight to be in contradiction to ordinary observations, for we are accustomed to see water standing on the surface of clay but not on humus. It must be borne in mind that clay, from its imperviousness, holds water like a vessel, the wa- ter remaining apparent; but humus retains it invisibly, its action being nearly like that of a sponge. One chief cause of the value of a layer of humus on the surface of the soil doubtless consists in this great re- taining power for water, and the success that has attended the practice of green manuring, as a means of renovating almost worthless shifting sands, is in a great degree to be attributed to this cause. The advantages of mulching are explained in the same way. Soils which are over-rich in humus, especially those of reclaimed peat-bogs, have some detrimental peculiarities deserving notice. . Stoeckhardt (Wéilda’s Centralblatt, 1858, 2, 22) examined the soil of a cultivated meor in Saxony, which, when moist, had an imbibing power of 60-69"|,. After being thoroughly dried, however, it lost its adhesiveness, and the imbibing power fell to 26-30" |,. It is observed in accordance with these data that such soils retain water late in spring; and when they become CHANGES OF THE BULK OF THE SOIL. 183 very dry in summer they are slow to take up water again, so that rain-water stands on the surface for a considerable time without penetrating, and when, after some days, it is soaked up, it remains injuriously long. Light rains after drought do little immediate good to such soils, while heavy rains always render them too wet and cold, unless they are suitably ameliorated. The same’is true to a less degree of heavy, compact clays. § 7 CHANGES OF THE BULK OF THE SOIL BY DRYING AND FROST. The Shrinking of Soils on Drying is a matter of no little practical importance. This shrinking is of course offset by an increase of bulk when the soil becomes wet. In variable weather we have therefore constant changes of volume occurring. Soils rich in humus experience these changes to the greatest degree. The surfaces of moors often rise and fall with the wet or dry season, through a space of sev- eral inches. In ordinary light soils, containing but little humus, no change of bulk is evident. Otherwise, it is in clay soils that shrinking is most perceptible; since these soils only dry superficially, they do not appear to settle much, but become full of cracks and rifts. Heavy clays may lose one-tenth or more of their volume on drying, and since at the same time they harden about the rootlets which are imbedded in them, it is plain that these indis- pensable organs of the plant must thereby be ruptured during the protracted dry weather. Sand, on the other hand, does not change its bulk by wetting or drying, and when present to a considerable extent in the soil, its par- ticles, being interposed between those of the clay, prevent the adhesion of the latter, so that, although a sandy loam ' shrinks not inconsiderably on drying, yet the lines of sepa- 184. : IlI0OW CROPS FEED. ration are vastly more numerous and less wide than in purer clays. Such a soil does not “cake,” but remains friable and powdery. Marly soils (containing carbonate of lime) are especially prone to fall toa fine powder during drying, since the carbonate of lime, which, like sand, shrinks very little, is itself in a state of extreme division, and therefore more effectually separates the clayey particles. The unequal shrinking of these two intimately mixed ingredients ac- complishes a perfect pulverization of such soils. On the cold, heavy soils of Upper Lusatia, in Germany, the appli- cation of lime has been attended with excellent results, and the larger share of the benefit is to be accounted for by the improvement in the texture of those soils which follows liming. The carbonate of lime is considerably soluble in water charged with carbonic acid, as is the wa- ter of a soil containing vegetable matter, and this agency of distribution, in connection with the mechanical opera- tions of tillage, must in a short time effect an intimate mixture of the lime with the whole soil. A tenacious clay is thus by a heavy liming made to approach the condition of a friable marl. Heaving by Frost.—Soils which imbibe much water, especially clay and peat soils, have likewise the disagree- able property of being heaved by frost. The expansion, by freezing, of the liquid water they contain, separates the particles of soil from each other, raises, in fact, the surface for a considerable height, and thus ruptures the roots of grass and especially of fall-sowed grain. The lifting of fence posts is due to the same cause. ¢ ? § 8. ADHESIVENESS OF THE SOIL. TIn the language of the farm a soil is said to be heavy or light, not as it weighs more or less, but as it is easy or ae . hal a ADHESIVENESS OF THE SOIL. 185 difficult to work. The state of dryness has great influence on this quality. Sand, lime, and humus have very little adhesion when dry, but considerable when wet. Soils in which they predominate are usually easy to work. But clay or impalpable matter has entirely different characters, upon which the tenacity of a soil almost exclusively de- pends. Dry “clay,” when powdered, has hardly more consistence than sand, but when thoroughly moistened its particles adhere together to a soft and plastic, but tena- cious mass; and in drying away, at a certain point it be- comes very hard, and requires a good deal of force to penetrate it. In this condition it offers great resistance to the instruments used in tillage, and when thrown up by the plow it forms lumps which require repeated harrow- ings to break them down. Since the adhesiveness of the soil depends so greatly upon the quantity of water con- tained in it, it follows that thorough draining, combined with deep tillage, whereby sooner or later the stiffest clays become readily permeable to water, must have the best effects in making such soils easy to work. The English practice of burning clays speedily accom- plishes the same purpose. When clay is burned and then crushed, the particles no longer adhere tenaciously to- gether on moistening, and the mass does not acquire again | the unctuous plasticity peculiar to unburned clay. Mixing sand with clay, or incorporating vegetable mat- ter with it, or liming, serves to separate the particles from each other, and thus remedies too great adhesiveness. The considerable expansion of water in the act of solid- ifying (one-fifteenth of its volume) has already been no- ticed as an agency in reducing rocks to powder. In the same way the alternate freezing and thawing of the water which impregnates the soil during the colder part of the year plays an important part in overcoming its adhesion. The effect is apparent in the spring, immediately after “the frost leaves the ground,” and is very considerable, 186 . HOW CROPS FEED. fully one-third of the resistance of a clay or loam to the plow thus disappearing, according to Schiibler’s experi- ments. Tillage, when carried on with the soil in a wet condi- tion, to some extent neutralizes the effects of frost, espe- cially in tenacious soils. Fall-plowing of stiff soils has been recommended, in order to expose them to the disintegrating effects of frost. § 9, RELATIONS OF THE SOIL TO HEAT. The relations of the soil to heat are of the utmost im- portance in affecting its fertility. The distribution of plants is, in general, determined by differences of mean temperature. In the same climate and locality, however, we find the farmer distinguishing between cold and warm soils. The Temperature of the Soil varies to a certain depth with that of the air; yet its changes occur more slowly, are confined to a considerably narrower range, and dimin- ish downward in rapidity and amount, until at a certain depth a point is reached where the temperature is invari- able. In summer the temperature of the soil is higher in day- time than that of the air; at night the temperature of the surface rapidly falls, especially when the sky is clear. In temperate climates, at a depth of three feet, the tem- perature remains unchanged from day to night; at a depth of 20 feet the annual temperature varies but a degree or two; at 75 feet below the surface, the chentacmins re- mains perfectly stationary. In the vaults of the Paris Observatory, 80 feet deep, the temperature is 50° Fahren- heit. In tropical regions the point of nearly inhi =~ temperature is reacled at a depth of one foot. RELATIONS OF THE SOIL TO HEAT. 187 The mean annual temperature of the soil is the same as, or in higher latitudes a degree above, that of the air. The nature and position of the soil must considerably influence its temperature Sources of the Heat of the Soil.—The sources of that heat which is found in the soil are three, viz.: First, the original heat of the earth; second, the chemical process of oxidation or decay going on within it; and third, an external one, the rays of the sun The earth has within itself a source of heat, which maintains its interior at a high temperature; but which escapes so rapidly from the surface that the soil would be constantly frozen but for the external supply of heat from the sun. The heat evolved by the decay of organic matters is not inconsiderable in porous soils containing much vegeta- ble remains; but decay cannot proceed rapidly until the external temperature has reached a point favorable to vegetation, and therefore this source of heat probably has no appreciable effect, one way or the other, on the welfare of the plant. The warmth of the soil, so far as it favors vegetable growth, appears then to depend exclusively on the heat of the sun. The direct rays of the sun are the immediate cause of the warmth of the earth’s surface. -The temperature of the soil near the surface changes progressively with the seasons; but at a certain depth the loss from the interior and the gain from the sun compensate each other, and, as has been previously mentioned, the temperature remains unchanged throughout the year. Daily Changes of Temperature.—During the day the sun’s heat reaches the earth directly, and is absorbed by the soil and the solid objects on its surface, and also by the air and water. But these different bodies, and also the different kinds of soil, have very different ability to absorb or become warmed by the sun’s heat. Air and 188 HOW CROPS FEED. water are almost incapable of being warmed by heat ap- plied above them. Through the air, heat radiates without being absorbed. Solid bodies which have dull and porous surfaces absorb heat most rapidly and abundantly. The soil and solid bodies become warmed according to their individual capacity, and from them the air receives the heat which warms it. From the moist surface of the soil goes on a rapid evaporation of water, which consumes * a large amount of heat, so that the temperature of the soil is not rapidly but gradually elevated. The ascent of wa- ter from the subsoil to supply the place of that evaporat- ed, goes on as before described. When the sun declines, the process diminishes in intensity, and when it sets, the reverse takes place. The heat that had accumulated on * When a piece of ice is placed in a vessel whose temperature is increasing, by means of a lamp, at the rate of one degree of the thermometer every minute, it will be found that the temperature of the ice rises until it attains 32°. When this point is reached, it begins to melt, but does not suddenly become fluid: the melting goes on very gradually. A thermometer placed in the water remains constantly at 32° so long asa fragment of ice is present. The moment the ice disappears, the temperature begins to rise again, at the rate of one degree per minute. The time during which the temperature of the ice and water remains at 32° is 140 minutes. During each of these minutes one degree of heat enters the mixture, but is not indicated by the thermometer—the mercury remains sta- tionary; 140° of heat have thus passed into the ice and become hidden, datent ; at the same time the solid ice has become liquid water. The difference, then, between ice and water consists in the heat that is latent in thelatter. If we now proceed with the above experiment, allowing the heat to increase with the same rapidity, we find that the temperature of the water rises constantly for 180 min- utes. The thermometer then indicates a temperature of 212°, (82-+180,) and the - water boils. Proceeding with the experiment, the water evaporates away, but the thermometer continues stationary so long as any liquid remains. After the - lapse of 972 minutes, it is completely evaporated. Water in becoming steam renders, therefore, still another portion, 972°, of heat latent. The heat latent in steam is indispensable to the existence of the latter. If this heat be removed by bringing the steam into a cold space, water is reproduced. If, by means of pressure or cold, steam be condensed, the heat originally latent in it becomes sensible, free, and capable of affecting the thermometer. If, also, water be con- verted into ice, as much heat is evolved and made sensible as was absorbed and made latent. It is seen thus that the processes of liquefaction and yaporization are cooling processes ; for the heat rendered latent by them must be derived from surrounding objects, and thus these become cooled. On the contrary, solidifica- tion, freezing, and vapor-condensation, are warming processes, sinee in them large quantities of heat cease to be latent and are made sensible, thus warming surrounding bodies. , RELATIONS OF THE SOIL TO HEAT. 189 the surface of the earth radiates into the cooler atmos- phere and planetary space; the temperature of the surface rapidly diminishes, and the air itself becomes cooler by convection.* As the cooling goes on, the vapor suspend- ed in the atmosphere begins to condense upon cool objects, while its latent heat becoming free hinders the too sudden reduction of temperature. The condensed water collects in drops—it is dew; or in the colder seasons it crystallizes as hoar-frost. The deposition of liquid water takes place not on the surface of the soil merely, but within it, and to that depth in which the temperature falls during the night, viz., 12 to 18 inches. (Krutzsch observed the temperature of a garden soil at the depth of one foot, to rise 8° F. ona May day, from 9 A: M. to 7 P. M.) Since the air contained in the interstices of the soil is at a little depth saturated with aqueous vapor, it results that the slightest reduction of temperature must at once occa- sion a deposition of water, so that the soil is thus supplied with moisture independently of its hygroscopic power. Conditions that Affect the Temperature of the Soil.— The special nature of the soil is closely connected with the maintenance of a uniform temperature, with the pre- vention of too great heat by day and cold by night, and with the watering of vegetation by means of dew. It is, however, in many cases only for a little space after seed- time that the soil is greatly concerned in these processes. So soon as it becomes covered with vegetation, the char- * Though liquids and gases are almost perfect non-conductors of heat, yet it can diffuse through them rapidly, if advantage be taken of the fact that by heating they expand and therefore become specifically lighter. If heat be applied to the upper surface of liquids or gases, they remain for a long time nearly unaffected ; if it be applied beneath them, the lower layers of particles become heated and rise, their place is supplied by others, and so currents upward and downward are established, whereby the heat is rapidly and uniformly distributed. This process of convection can rarely have any influence én the soil. What we have stated concerning it shows, however, in what way the atmosphere may constantly act in removing heat from the surface of the soil. 190 HOW CROPS FEED. acter of the latter determines to a certain degree the na- ture of the atmospheric changes. In case of many crops, the soil is but partially covered, and its peculiarities aré then of direct influence on its temperature. Relation of Temperature to Color and Texture.—It is usually stated that black or dark-colored soils are sooner warmed by the sun’s rays than those of lighter color, and remain constantly of a higher temperature so long as the sun acts on them. An elevation of several degrees in the temperature of a light-colored soil may be caused by strewing its surface with peat, charcoal powder, or vege- table mould. To this influence may be partly ascribed the following facts. Lampadius was able to ripen melons, even in the coolest summers, in Freiberg, Saxony, by strewing a coating of coal dust an inch deep over the sur- face of the soil. In Belgium and on the Rhine, it is found that the grape matures best, when the soil is covered with fragments of black clay slate. According to Creuzé-Latouche, the vineyards along the river Loire grow either upon a light-colored calcareous soil, or upon a dark red earth. These two kinds of soil often alternate with each other within a little distance, and the character of the wine produced on them is remark- ably connected with the color of the earth. On the light- colored soils only a weak, white wine can be raised to ad- vantage, while on contiguous dark soils a strong claret of fine quality is made. (Gasparin, Cours @ Agriculture, 1, 103.) | | . Girardin found in a series of experiments on ‘the cultiva- tion of potatoes, that the time of their ripening varied eight to fourteen days, according to the color of the soil. He found on August 25th, in a very dark humus soil, twenty-six varieties ripe; in sandy soil, twenty; in clay, nineteen; and in white lime soil, only sixteen. It is not difficult, however, to indicate other causes that will ac- count in part for the results of Girardin. RELATIONS OF THE SOIL TO HEAT. 191 Schiibler made observations on the temperatures at- tained by various dry soils exposed to the sun’s rays, according as their surfaces were blackened by a thin sprinkling of lamp-black or whitened by magnesia. His results are given in columns 1 and 2 of the following table (vide p. 196,) from which it is seen that the dark surface was warmed 13° to 14° more than the white. We like- wise notice that the character of the very surface deter- mines the degree of warmth, for, under a sprinkling of lamp-black or magnesia, all the soils experimented with became as good as identical in their absorbing power for the sun’s heat. The observations of Malaguti and Durocher prove that the peculiar temperature of the soil is not always so closely related to color as to other qualities. They studied the thermometric characters of the following soils, viz.: Garden earth of dark gray color,—a mixture of sand and gravel with about five per cent of humus; a grayish- white quartz sand; a grayish-brown granite sand; a fine light-gray clay (pipe clay); a yellow sandy clay; and, finally, four lime soils of different physical qualities. It was found that when the exposure was alike, the dark-gray granite sand became the warmest, and next to this the grayish-white quartz sand. The latter, notwith- standing its lighter color, often acquired a higher temper- ature at a depth of four inches than the former, a fact to be ascribed to its better conducting power. The black soils never became so warm as the two just mentioned. After the black soils, the others came in the following or- der: garden soil; yellow sandy clay; pipe clay; lime soils having crystalline grains; and, lastly, a pulverulent chalk soil. To show what different degrees of warmth soils may acquire, under the same circumstances, the following max- imum temperatures may be adduced: At noon of a July day, when the temperature of the air was 90°, a thermom- 192 HOW CROPS FEED. eter placed at a depth of a little more than one inch, gave these results: PAULA SINT |y. 5 us... saute ssc sigee de hoe awe wets eee 126° Fprerystalline lime soil. . ...43..'50;.5 sek sewers Mfar Pa oarden Soil. 0. .6.). cy .sibs ae ta ep ono wei ole hale ee 114° imyellow sandy (clay... ... soci se ow wee. fetsievetanete tater 100° AA THOR CLANS s'. oes Sess chan sens satel see aoe See 94° ita Clvalik “BOM. is Fei. 0'eie dina fas Fer delale a eee pee Oe ee ee 8z Here we observe a difference of nearly 40° in the noon- day temperature of the coarse quartz and the chalk soil. Malaguti and Durocher found that the temperature of the garden soil, just below the surface, was,‘on the average of day and night together, 6° Fahrenheit higher than that of the air, but that this higher temperature diminished at a greater depth. A thermometer buried four inches indi- cated a mean temperature only 3° above that of the at- mosphere. The experimenters do not mention the influence of wa- ter in affecting these results; they do not state the degree of dryness of these soils. It will be seen, however, that the warmest soils are those that retain least water, and doubtless something of the slowness with which the fine soils increase in warmth is connected with the fact that they retain much water, which, in evaporating, appropri- ates and renders latent a large quantity of heat. The chalk goil is seen to be the coolest of all, its tem- perature in these observations being three degrees lower than that of the atmosphere at noonday. In hot climates this coolness is sometimes of great advantage, as appears to happen in Spain, near Cadiz, where the Sherry vine- yards flourish. “The Don said the Sherry wine district ~ was very small, not more than twelve miles square. The ~ Sherry grape grew only on certain low, chalky hills, where the earth being light-colored, is not so much burnt; did — not chap and split so much by the sun as darker and heavier soils do. A mile beyond these hills the grape de- teriorates.”—(Dickens’ Household Words, Nov. 13, 1858.) RELATIONS OF THE SOIL TO HEAT. 193 - In Explanation of these observations we must recall to mind the fact that all bodies are capable of absorbing and radiating as well as reflecting heat. These properties, al- though never dissociated from color, are not tiecessarily dependent upon it. They chiefly depend upon the char- acter of the surface of bodies. Smooth, polished surfaces absorb and radiate heat least readily; they reflect it most perfectly. Radiation and absorption are opposed to each other, and the power of any body to radiate, is precisely equal to its faculty of absorbing heat. It must be understood, however, that bodies may differ in their power of absorbing or radiating heat of different degrees of intensity. Lamp-black absorbs and radiates heat of all intensities in the same degree. White-lead absorbs heat of low intensity (such as radiates from a ves- sel filled with boiling water) as fully as lamp-black, but of the intense heat of a lamp it absorbs only about one- half as much. Snow seems to resemble white-lead in this respect. Ifa black cloth or black paper be spread on the surface of snow, upon which the sun is shining, it will melt much faster under the cloth than elsewhere, and this, too, if the cloth be not in contact with, but suspended above, the snow. In our latitude every one has had op- portunity to observe that snow thaws most rapidly when covered by or lying on black earth. The people of Cham- ouni, in the Swiss Alps, strew the surface of their fields with black-slate powder to hasten the melting of the snow. The reason is that snow absorbs heat of low intensity with greatest facility. The heat of the sun is converted from a high to a low intensity by being absorbed and then radiated by the black material. But it is not color that determines this difference of absorptive power, for indigo and Prussian blue, though of nearly the same color, have very different absorptive powers. So far, however, as our observations extend, it appears that, usually, dark-colored soils absorb heat most rapidly, and that the sun’s rays 9 194 , HOW CROPS FEED. have least effect on light-colored soils. (See the table on p. 196.) The Rapidity of Change of Temperature sa lependenale of color or moisture has been determined on a number of soils by Schiibler. A given volume of dry soil was heat- ed to 145°, a thermometer was placed in it, and the time was observed which it required to cool down to 70°, the temperature of the atmosphere being 61°. The subjoined table gives his results. In one column are stated the times of cooling, in another the relative power of retaining heat or capacity for heat, that of lime sand being assumed as 100. ROMO CBO oop 3 nox Gio oe os aR etls RR 3 hours 80: minlewenas 100 EPUTU RP RCO 1 aa Peete payee Seeeatenateee 3 SOOT 95.6 PMR SCA oo ake sou. oe lee’ oe Re A OS omens 76.9 WSN eee eS. Sed Oe ee eee Q. 6 > BA SSR ees ee 73.8 Only TEL i Lea tlge was pale mares 2 a8 (4:80. Seen 71.8 Sclays TO WATE: Slade we sick Mos eer Bote B08 20) Woe 70.1 PAE AMID So Sa Shee Se ccs eee te ces Bo a “Sa aeeee 68.4. 1&1 he CB 5 ict ya): 6 aR ce era Ap 2.1) 10) ae 66.7 ace Car ithe <3 ¢2 qasled seins do setae bes By D6 jee eee 64.8. INEM WAP DIGS w'5 ou: eae og ae eget Db SO ee 61.3 PAMUNS oe Scouse alee toes oe ee eee 1. (8 a er 49.0 Lr Tig BUSS AS Slog Opel Sa PESOS. er (5 A Tio “20 ae 38.0 It is seen that the sandy soils cool most slowly, then follow clays and heavy soils, and lastly comes humus. The order of cooling above given is in all respects identical with that of warming, provided the circumstances are alike. In other words these soils, containing no moist- ure, or but little, and exposed to heat of low intensity, would be raised through a given range of temperature in the same relative times that aoe fall through a given number of degrees. | Itisto be particularly noticed that dark humus and white magnesia are very closely alike in their rate of cooling, and cool rapidly; while white lime sand stands at the op- posite extreme, requiring twice as long to cool to the same extent. These facts strikingly illustrate the great differ- ee RELATIONS OF THE SOIL TO HEAT. 195 ence between the absorption of radiant heat of low inten- sity or its,;communication by conduction on one hand, and that of high intensity like the heat of the sun on the other. Retention of Heat.—Other circumstances being equal, the power of retaining heat (slowness of cooling) is the greater, the greater the weight of a given bulk of soil, i. e., the larger and denser its particles. A soil covered with gravel cools much more slowly than a sandy surface, and the heat which it collects durmg a sunny day it carries farther into the night ; hence gravelly soils are adapted for such crops as are liable to fail of rip- ening in cool situations, especially grapes, as has been abundantly observed in practice. Color is without influence on the loss of heat from the soil by radiation, because the heat is of low intensity. The porosity or roughness of the surface (extent of sur- face) determines cooling from this cause. Dew, which is deposited as the result of cooling by radiation of heat into the sky, forms abundantly on grass and growing vege- tation, and on vegetable mould, but is more rarely met mah on coarse sand or gravel. Influence of Moisture on the Temperature of the Soil. —All soils, when thoroughly wet, seem to be nearly alike in their power of absorbing and retaining warmth. This is due to the fact that the capacity of water for heat is much greater than that of the soil. We have seen that lime sand and quartz sand are the slowest of all the in- gredients of soils to suffer changes of temperature when exposed to a given source of heat. (See table, p. 194.) Now, water is nine times slower than quartz in being affected by changes of temperature, and as the entire sur- face of the wet soil is water, which is, besides, a nearly perfect non-conductor of heat, we can understand that ex- ternal warmth must affect it slowly. Again, the immense consumption of heat in the forma- tion of vapor (see note, p. 188) must prevent the wet soil 196 HOW CROPS FEED. from ever acquiring the temperature it shortly attains when dry. rr From this cause the difference in temperature between dry and wet soil may often amount to from 10° to 18°. — On this point, again, Schiibler furnishes us with the re- sults of his experiments. Columns 4 and 5 in the table below give the temperatures which the thermometer at- tained when its bulb was immersed in various soils, both wet and dry, each having its natural color. (Columns 1 and 2 are referred to on p. 191.) 2 3 4 5 6 Surface. Surface. Gama ip Whit-|Black- Diff Differ Jhit-| Black-—|Differ- iffer- ened.} ened. | ence. Wet. | Dry. ence, Magnesia, pure white........./.....:. 108.'%°| 121.8°} 12.6° | 95:2°) 108-77 ))4aias Fine carbonate of lime, white......... 109.2°} 122.9°].13.7° | 96.1°} 109.4°) 13.3° Gypsum, bright white-gray............ 110.3°| 124.3°}. 14.0° |. 97%.3°} 110.5°| 13.2° OM eNO DEAN es sie stteeteg co cise st 107.6°| 122.0°) 14.4° | 97.'7°| 1110-72) D4508 Nandy, Clay vellOwilGh .+ vcs teeccss cee 108.3°} 121.6°) 13.3° | 98.2°) 111.4°| 13.2% Quartz sand, bright yellowish-gray....|109.9°| 123.6°| 13.7° | 99.1°| 112.6°| 13.5° MSO meV ECOWAS Die cies sere Se roa icsmee ie cise 107.8°| 121.1°| 13.3° | '99-1°) T12ats te Lime sand, whitish-gray.............. 109.9°) 124.0°} 14.1° | 99.3°| 112.17] 12.85 Heavy clay soil, yellowish-gray........ 107.4°) 120.4°} 13.0° | 99.3°| 112.3°| 13.0° sre clay “nluish-oray.: Fs. J 2.6 se scje0e )106.3°| 120.0°) 13.7° | 99.5°| 1138.0°| 13.5° Garden mould, blackish-gray.......... 108 .3°} 122.5°| 14.2° | 99.5°) 118.5°) 140° Slaty marl, brownish-red.............. 108-3°| 128 .4°) 15.1° 1101.8") 115782) Daaae Humus, brownish-black............... 108.5°| 120.9°| 12.4° |103.6°| 11%.3°| 13.7° We note that the difference in favor of the dry earth is almost uniformly 13° to 14°. This difference is the same as observed between the whitened and blackened speci- mens of the same soils. (Column 3.) | We observe, however, that the wet soil in no case be- comes as warm as the same soil whitened. We notice further that of the wet soils, the dark-colored ones, humus and marl, are most highly heated. Further it is seen that coarse lime sand (carbonate of lime) acquires 3° higher [temperature than fine carbonate of lime, both wet, prob- ably because evaporation proceeded more slowly from the coarse than from the fine materials. Again it is plain on comparing columns 1, 2, and 5, that the gray to yellowish brown and black colors of all the soils, save the first three, assist the elevation of temperature, which rises nearly RELATIONS OF THE SOIL TO HEAT. 197 with the deepening of the color, until in case of humus it lacks but a few degrees of reaching the warmth of a sur- face of lamp-black. According to the observations of Dickinson, made at Abbot’s Hill, Hertfordshire, England, and continued through eight years, 90 per cent of the water falling be- tween April Ist and October 1st evaporates from the sur- face of the soil, only 10 per cent finding its way into drains laid three and four feet deep. The total quantity of water that fell during this time amounted to about 2,900,000 Ibs. per acre; of this more than 2,600,000 evap- orated from the surface. It has been calculated that to evaporate artificially this enormous mass of water, more than seventy-five tons of coal must be consumed. Thorough draining, by loosening the soil and causing a rapid removal from below of the surplus water, has a most decided influence, especially in spring time, in warming the soil and bringing it into @ suitable condition for the support of vegetation. It is plain, then, that even if we knew with accuracy what are the physical characters of a surface soil, and if we were able to estimate correctly the influence of these characters on its fertility, still we must investigate those circumstances which affect its wetness or dryness, whether they be an impervious subsoil, or springs coming to the surface, or the amount and frequency of rain-falls, taken in connection with other meteorological causes. We can- not decide that a clay is too wet or a sand too dry, until we know its situation and the climate it is subjected to. The great deserts of the globe do not owe their barren- ness to necessary poverty of soil, but to meteorological influences—to the continued prevalence of parching winds, and the absence of mountains, to condense the atmospheric water and establish a system of rivers and streams. This is not the place to enter into a discussion of the causes that may determine or modify climate; but to illustrate 198 HOW CROPS FEED. the effect that may be produced by means within human control, it may be stated that previous to the year 1821, the French district Provence was a fertile and well-water- ed region. In 1822, the olive trees which were largely cultivated there were injured by frost, and the inhabitants began to cut them up root and branch. This amounted to clearing off a forest, and, in consequence, the streams dried up, and the productiveness of the country was seri- ously diminished. The Angle at which the Sun’s Rays Strike a Soil is of great influence on its temperature. The more this ap- proaches a right angle the greater the heating effect. In the latitude of England the sun’s heat acts most power- fully on surfaces having a southern exposure, and which are inclined at an angle of 25° and 30°. The best vine- yards of the Rhine and Neckar are also on hill-sides, so situated. In Lapland and Spitzbergen the southern side of hills may be seen covered with vegetation, while lasting or even perpetual snow lies on their northern in- clinations. . The Influence of a Wall or other Reflecting Surface upon the warmth of a soil lying to the south of it was observed in the case of garden soil by Malaguti and Durocher. The highest temperature indicated by a ther- mometer placed in this soil at.a distance of six inches from the wall, during a series of observations lasting seven days (April, 1852), was 32° Fahrenheit higher at the surface, and 18° higher at a depth of four inches than in the same soil on the north side of the wall. The average temper- ature of the former during this time was 8° higher than that of the latter. In another trial in March the difference in average temperature between the southern and north- ern exposures was nearly double this amount in favor of the former. As is well known, fruits which refuse to ripen in cold climates under ordinary conditions of exposure may attain THE FREE WATER OF THE SOIL. 199 perfection when trained against the sunny side of a wall. It is thus that in the north of England pears and plums are raised in the most unfavorable seasons, and that the vineyards of Fontainebleau produce such delicious Chas- selas grapes for the Paris market, the vines being trained against walls on the Thomery system. In the Rhine district grape vines are kept low and as near the soil as possible, so that the heat of the sun may be reflected back upon them from the ground, and the ripen- ing is then carried through the nights by the heat radiated from the earth.—(Journal Highland and Agricultural Society, July, 1858, p. 347.) Vegetation.— Malaguti and Durocher also studied the effect of a sod on the temperature of the soil. They ob- served that it hindered the warming of the soil, and in- deed to about the same extent as a layer of earth of three inches depth. Thus a thermometer four inches deep in green-sward acquires the same temperature as one seven inches deep in the same soil not grassed. CHAPTER V. THE SOIL AS A SOURCE OF FOOD TO CROPS.— INGREDIENTS WHOSE ELEMENTS ARE OF ATMOSPHERIC ORIGIN. si THE FREE WATER OF THE SOIL IN ITS RELATIONS TO VEGETABLE NUTRITION. Water may exist free in the soil in three conditions, which we designate respectively hydrostatic, capillary, and hygroscopic. Hydrostatic or Flowing * Water is water visible as * I, e., capable of flowing. 200 HOW CROPS FEED. such to the eye, and free to obey the laws of gravity and motion. When the soil is saturated by rains, melting snows, or by overflow of streams, its pores contain hy- drostatic water, which sooner or later sinks away into the subsoil or escapes into drains, streams, or lower situations. Bottom Water is permanent hydrostatic water, reached nearly always in excavating deep soils. The surface of water in a well corresponds with, or is somewhat below, the upper limit of bottom water. It usually fluctuates in level, rising nearer the surface of the soil in wet seasons, and receding during drought. In general, agricultural plants are injured if their roots be immersed for any length of time in hydrostatic water; and soils in which bottom water is found at a little depth during the season of growth are unprofitable for culture. If this depth be but a few inches, we have a bog, swamp, or swale. If it is one and a half to three feet, and the surface soil be light, gravelly, or open, so as to admit of rapid evaporation, some plants, especially grasses, may flourish. If at a constant depth of four to eight feet under a gravelly or light loamy soil, it is favorable to crops as an abundant source of water. Heavy clays, which retain hydrostatic water for a long time, being but little permeable, are for the same reasons unfavorable to most crops, unless artificial provision be made for removing the excess. Rice, as we have seen, (H. C. G., p. 252), is a plant which grows well with its roots situated in water. Hen- rici’s experiment with the raspberry (H. C. G., p. 254), and the frequent finding of roots of clover, turnips, ete., in cisterns or drain pipes, indicate that many or all agricultural plants may send down roots into the bottom water for the purpose of gathering a sufficient supply of | this necessary liquid. Capillary Water is that which is held in the fine pores of the soil by the surface attraction of its particles, as oil . | THE FREE WATER OF THE SOIL. 201 is held in the wick of alamp. The adhesion of the water to the particles of earth suspends the flow of the liquid, and it isno longer subject to the laws of hydrostatics. Capillary water is usually designated as moisture, though a soil saturated with capillary water would be, in most cases, wet. The capillary power of various soils has al- ready been noticed, and is for coarse sands 25°|,; for loams and clays, 40 to 70°|,; for garden mould and humus, much higher, 90 to 300 °|,. (See p. 180.) 7 For a certain distance above bottom water, the soil is saturated with capillary water, and this distance is the greater, the greater the capillary power of the soil, 1. e., the finer its pores. Capillary water is not visible as a distinct liquid layer on or between the particles of soil, but is still recogniza- ble by the eye. Even in the driest weather and in the driest sand (that is, when not shut off from bottom water by too great distance or an intervening gravelly subsoil) it may be found one or a few inches below the surface where the soil looks motst—has a darker shade of color. Hygroscopic Water is that which is not perceptible to the senses, but is appreciated by loss or gain of weight in ‘the body which acquires or is deprived of it. (H.C. G., p- 54.) The loss experienced by an air-dry soil when kept for some hours at, or slightly above, the boiling point (212° F.,) expresses its content of hygroscopic water. This quantity is variable according to the character of the soil, and is constantly varying with the temperature; in- creasing during the night when it is collected from the at- mosphere, and diminishing during the day when it returns in part to the air. (Seep. 164.) The amount of hygros- copic water ranges from 0.5 to 10 or more per cent. Value of these Distinctions.—These distinctions be- tween hydrostatic, capillary, and hygroscopic water, are nothing absolute, but rather those of degree. Hygroscopic water is capillary in all respects, save that its quantity is 202 HOW CROPS FEED. small, and its adhesion to the particles of soil more firm for that reason. Again, no precise boundary can always” be drawn between capillary and hydrostatic water, espe- cially in soil having fine pores. The terms are neverthe- less useful in conveying an idea of the degrees of wet- ness or moisture in the soil. Roots Absorb Capillary or Hygroscopic Water.—It is from capillary or hygroscopic water that the roots of most agricultural plants chiefly draw a supply of this liquid, though not infrequently they send roots into wells and drains. The physical characters of soils that have been already considered suffice to explain how the earth acquires this water; it here remains to notice how the plant is re- lated to it. As we have seen (pp. 35-38), the aerial organs appear incapable of taking up either vapor or liquid water from the air to much extent, ‘and even roots continually exhale vapor without absorbing any, or at least without being able to make up the loss which they continually suffer. Transpiration of Water through Plants.—It is a most familiar fact that water constantly exhales from the surface of. the plant. The amount of this exhalation is often very great. Hales, the earliest observer of this phenomenon, found that a sunflower whose foliage had 39 square feet of surface, gave off in 24 hours 3 lbs. of water. A cab- bage, whose surface of leaves equaled 19 square feet, ex- haled in the same time very nearly as much. Schleiden found the loss of water from a square foot of grass-sod to be more than it Ibs. in 24 hours. Schiibler states that in the same time 1 square foot of pasture-grass exhaled nearly 54 lbs. of water. In oneseof Knop’s more recent experiments, (Vs. Sé., VI, 239), a dwarf bean exhaled during 23 days, in September and October, 13 times its weight of water. In another trial a maize-plant transpir- ed 36 times its weight of water, from May 22d to Sept. 4th. According to Knop, a grass-plant will exhale its own THE FREE WATER OF THE SOIL. 203 weight of water in 24 hours of hot and dry summer weather. : The'water exhaled from the leaves must be constantly supplied by absorption at the roots, else the foliage soon becomes flabby or wilts, and finally dies. Except so far as water is actually formed or fixed within the plant, its absorption at the roots, its passage through the tissues, and its exhalation from the foliage, are nearly equal in quantity and mutually dependent during the healthy ex- istence of vegetation. Circumstances that Influence Transpiration.—a. The structure of the leaf, including the character of the epi- dermis, and the number of stomata as they affect exhala- tion, has been considered in ‘How Crops Grow,” (pp. 286-8). b. The physical conditions which facilitate evapora- tion increase the amount of water that passes through the plant. LExhalation of water-vapor proceeds most rapidly in a hot, dry, windy summer day. It is nearly checked when the air is saturated with moisture, and va- ries through a wide range according to the conditions just named, c. The oxidations that are constantly going on within the plant may, under certain conditions, acquire sufficient intensity to develop a perceptible amount of heat and cause the vaporization of water. It has been repeatedly noticed that the process of flowering is accompanied by considerable elevation of temperature, (p. 24). In general, however, the opposite process of deoxidation preponder- ates with the plant, and this must occasion a reduction of temperature. These interior changes can have no apprecia- ble influence upon transpiration as compared with those that depend upon external causes. Sachs. found in some of his experiments (p. 36) that exhalation took place from plants confined in a limited space over water. Sachs be- 204 HOW CROPS FEED. lieved that the air surrounding the plants in these experi- ments was saturated with vapor of water, and concluded that heat was developed within the plant, which caused vaporization. More recently, Boehm (Sitzungsberichte der Wiener Akad., XUVIII, 15) has made probable that the air was not fully or constantly saturated with moist- ure in these experiments, and by taking greater precau- tions has arrived at the conclusion that transpiration abso- lutely ceases in air saturated with aqueous vapor. d. The condition of the tissues of the plant, as depend- ent upon their age and vegetative activity, likewise has a marked effect on transpiration. Lawes* and Knop both found that young plants lose more water than older ones. This is due to the diminished power of mature foliage to imbibe and contain water, its cells becoming choked up with growth and inactive. e. The character of the medium in which the roots are situated also remarkably influences the rate of transpira- tion. This fact, first observed by Mr. Lawes, in 1850, Joe. cit., Was more distinctly brought out by Dr. Sachs at a later period. (Vs. S¢., I, p. 203.) Sachs experimented on various plants, viz.: - beans, squashes, tobacco, and maize, and observed their transpi- ration in weak solutions (mostly containing one per cent) of nitre, common salt, gypsum, (one-fifth per cent solu- tion) and sulphate of ammonia. He also experimented with maize in a mixed solution of phosphate and silicate of potash, sulphates of lime and magnesia, and common salt, and likewise observed the effect of free nitric acid and free potash on the squash plant. The young plants were either germinated in the soil, then removed from it and set with their rootlets in the solution, or else were kept in the soil and watered with the solution. The glass . * Kauperimental Investigation into the Amount of Water given off by Plants during their Growth, by J. B. Lawes, of Rothamstead, London, 1850. THE FREE WATER OF THE SOIL. 205 vessel containing the plant and solution was closed above, around the stem of the plant, by glass plates and cement, so that no loss of water could occur except through the plant itself, and this loss was ascertained by daily weigh- ings. The result was that all the solutions mentioned, except that of free nitric acid, quite uniformly retarded transpiration to a degree varying from 10 to 90 per cent, while the free acid accelerated the transpiration in a cor- responding manner. Sachs experimented also with four tobacco plants, two situated in coarse sand and two in yellow loam. The plants stood side by side exposed to the same temperature, etc., and daily weighings were made during a week or more, to learn the amount of exhalation. The result was that the total loss, as well as the daily loss in the majority of weighings, was greater from the plant growing in loam, although through certain short periods the opposite was noticed. J. The temperature of the soil considerably affects the rate of transpiration by influencing the amount of absorp- tion at the roots. Sachs made a number of weighings up- on two tobacco plants of equal size, potted in portions of the same soil and having their foliage exposed to the same atmosphere. After observing their relative transpiration when their roots were at the same temperature, one pot was warmed a number of degrees, and the result was in- variably observed that elevating the temperature of the soil increased the transpiration. The same observer subsequently noticed the entire sup- pression of absorption by a reduction of temperature to 41° to 48° F. A number of healthy tobacco and squash plants, rooted in a soil kept nearly saturated with water, | were: growing late in November in a room, the tempera- ture of which fell at night to the point just named. In the morning the leaves of these plants were so wilted that they hung down like wet cloths, as if the soil were 206 HOW CROPS FEED. completely dry, or they had been fora long time acted upon by a powerful sun. Since, however, the soil was moist, the wilting could only arise from the inability of the roots to absorb water as rapidly as it exhaled from the leaves, owing to the low temperature. Further ex- periments showed that warming the soil in which the wilted plants stood, restored the foliage to its proper tur- gidity in a short time, and by surrounding the soil of a fresh plant with snow, the leaves wilted in three or four hours. Cabbages, winter colza, and beans, similarly circum- stanced, did not-wilt, showing that different plants are un- equally affected. The general rule nevertheless appears to be established that within certain limits the root absorbs more vigorously at high than at low temperatures, The Amount of Loss of Water of Vegetation in Wilt- ing has been determined by Hesse (Vs. S¢., I, 248) in case of sugar-beet leaves. Of two similar leaves, one, gathered at evening after several days of dryness and sun- shine, contained 85.74°|, of water; the other, gathered the next morning, two hours after a rain storm, yielded 89.57°|,. The difference was accordingly 3.8°|,. Other observations corroborated this result. Is Exhalation Indispensable to Plants ?—It was for along time supposed that transpiration is indispensable to the life of plants. It was taught that the water which the plant imbibes from the soil to replace that lost by ex- halation, is the means of bringing into its roots the min- eral and other soluble substances that serve for its nutri- ment. There are, however, strong grounds for believing that the current of water which ascends through a plant moves independently of the matters that may be in solution, either without or within it; and, moreover, the motion of soluble matters from the soil into the plant may go on, THE FREE WATER OF THE SOIL. 207 although there be no ascending aqueous current. (H. C. G., pp. 288 and 340.) - In accordance with these views, vegetation grows as well in the confined atmosphere of green-houses or of Wardian Cases, where the air is for the most part or entirely satu- rated with vapor, so that transpiration is reduced to a mini- mum, as in the free air, where it may attain a maximum. As is well known, the growth of field crops and garden vegetables is often most rapid during damp and showery weather, when the transpiration must proceed with com- parative slowness. While the above considerations, together with the asser- tion of Knop, that leaves lose for the first half hour nearly the same quantities of water under similar exposure, whether they are attached to the stem or removed from it, whether entire or in fragments, would lead to the con- clusion that transpiration, which is so extremely variable in its amount, is, so to speak, an accident to the plant and not a process essential to its existence or welfare, there are, on the other hand, facts which appear to indicate the contrary. In certain experiments of Sachs, in which the roots of a bean were situated in an atmosphere nearly saturated with aqueous vapor, the foliage being exposed to the air, although the plant continued for two months fresh and healthy to appearance, it remained entirely stationary in its development. (Vs. Sé., I, 237.) Knop also mentions incidentally (Vs. Sé., I, 192) that beans, lupines, and maize, die when the whole plant is kept confined in a vessel over water. It is not, however, improbable that the cessation of growth in the one case and the death of the plants in the other were due not so much to the checking of transpira- tion, which, as we have seen, is never entirely suppressed under these circumstances, as to the exhaustion of oxygen or the undue accumulation of carbonic acid in the narrow 208 HOW CROPS FEED, and confined atmosphere in which these results were noticed, On the whole, then, we conclude from the evidence be- fore us that transpiration is not necessary to vegetation, or at least fulfills no very important offices in the nutrition of plants. The entrance of water into the plant and the steady maintenance of its proper content of this substance, under all circumstances is of the utmost moment, and leads us to notice in the next place the Direct Proof that Crops can Absorb from the Soil enough Hygroscopic Water to Maintain their Life.—Sachs suffered a young bean-plant standing in a pot of very reten- tive (clay) soil to remain without watering until the leaves began to wilt. A high and spacious glass cylinder, having a layer of water at its bottom, was then provided, and the pot containing the wilting plant was supported in it, near its top, while the cylinder was capped by two semicircular plates of glass which closed snugly about the stem of the bean. The pot of soil and the roots of the plant were thus enclosed in an atmosphere which was constantly sat- urated, or nearly so, with watery vapor, while the leaves were fully exposed to the free air. It was now to be ob- served whether the water that exhaled from the leaves could be supplied by the hygroscopic moisture which the soil should gather from the damp air enveloping it. This proved to be the case. The leaves, previously wilted, re- covered their proper turgidity, and remained fresh during the two months of June and July. Sachs, having shown in other experiments that plants situated precisely like this bean, save that the roots are not — in contact with soil, lose water continuously and have no power to recover it from damp air (p. 86) thus gives us demonstration that the clay soil which condenses vapor in its pores and holds it as hygroscopic water, yields it again ~ to the plant, and thus becomes the medium through which THE FREE WATER OF THE SOIL. 209 water is continually carried from the atmosphere into vegetation. In a similar experiment, a tobacco plant was employed which stood in a soil of humus. This material was also capable of supplying the plant with water by virtue of its hygroscopic power, but less satisfactorily than the clay. As already mentioned, these plants, while remaining fresh, exhibited no signs of growth. This may be due to the consumption of oxygen by the roots and soil, or possibly the roots of plants may require an occasional drenching with liquid water. Further investigations in this direc- tion are required and promise most interesting results. What Proportion of the Capillary and Hygroscopic Water of the Soil may Plants Absorb, is a question that Dr. Sachs has made the only attempts to answer. When a plant, whose leaves are in.a very moist atmosphere, wilts or begins to wilt in the night time, when therefore trans- piration is reduced to a minimum, it is because the soil no longer yields it water. The quantity of water still con- tained in a soil at that juncture is that which the plant cannot remove from it,—is that which is unavailable to vegetation, or at least to the kind of vegetation experi- mented with. Sachs made trials on this principle with tobacco plants in three different soils. The plant began to wilt in a mixture of black humus (from beech-wood) and sand, when the soil contained 12.3°|, of water.* This soil, however, was capable of holding 46°|, of capillary water. It results therefore that of its highest content of absorbed water 33.7°|, (=46—12.3) was available to the tobacco plant. Another plant began to wilt on a rainy night, while the loam it stood in contained 8°], of water. This soil was able to absorb 52.1°|, of water, so that it might after * Ascertained by drying at 212°, 210 HOW CROPS FEED. saturation, furnish the tobacco plant with 44,1°| weight of water. A coarse sand that could hold 20.8°|, of water was found to yield all but 1.5°|, to a tobacco plant. From these trials we gather with at least approximate accuracy the power of the plant to extract water from these several soils, and by difference, the quantity of wa- ter in them that was unavailable to the tobacco plant. How do the Roots take Hygroscopic Water from the Soil ?—The entire plant, when living, is itself extremely hygroscopic. Even the dead plant retains a certain pro- portion of water with great obstinacy. Thus wheat, maize, starch, straw, and most air-dry vegetable substances, contain 12 to 15°|, of water; and when these matters are exposed to damp air, they can take up much more. Ac- cording to Trommer (Bodenkunde, p. 270), 100 parts of the following matters, when dry, absorb from moist air in 12 Bd) ag of its 0 eA ENE ee hours. Fine cut barley straw, 15 24 o4 45 parts of water. 66 73 rye ce 12 90 OF 99 “ cc ee ‘ - «6 white unsized paper, 8 12 17: Qs Coe As already explained, a body is hygroscopic because there is attraction between its particles and the particles of water. The form of attraction exerted thus among different kinds of matter is termed adhesive attraction, or simply adhesion. Adhesion acts only through a small distance, but its in- tensity varies greatly within this distance. If we attempt to remove hygroscopic water from starch or any similar body by drying at 212°, we shall find that the greater part of the moisture is easily expelled in a short time, but we shall also notice that it requires a relatively much longer time to expel the last portions. A general law of attraction is that its force diminishes as the distance be- tween the attracting bodies increases. This has been ex- THE FREE WATER OF THE SOIL. 211 actly demonstrated in case of the force of gravity and electrical attraction, which act through great intervals of space. We must therefore suppose that when amass of hygro- scopic matter is allowed to coat itself with water by the exercise of its adhesive attraction, the layer of aqueous particles which is in nearest contact is more strongly held - to it than the next outer layer, and the adhesion diminish- es with the distance, until, at a certain point, still too small for us to perceive, the attraction is nothing, or is’ neutralized by other opposing forces, and further adhesion ceases. Suppose, now, we bring in contact at a single point two masses of the same kind of matter, one of which is satu- rated with hygroscopic water and the other is perfectly dry. It is plain that the outer layers of water-particles adhering to the moist body come at once within the range of a more powerful attraction exerted by the very surface of the dry body. The external particles of water attached to the first must then pass to the second, and they must also distribute themselves equally over the surface of the latter; and this motion must go on until the attraction of the two surfaces is equally satisfied, and the water is equally distributed according to the surface, i. e., 1s uni- form over the whole surface. If of two different bodies put in contact (one dry and one moist) the surfaces be equal, but the attractive force of one for water be twice that of the other, then motion must go on until the one has appropriated two-thirds, and the other is left with one-third the total amount of water. When bodies in contact have thus equalized the water at their disposal, they may be said to be in a condition of hygroscopic equilibrium. Any cause which disturbs this equilibrium at once sets up motion of the hygroscopic water, which always proceeds from the more dry to the less dry body. 912 HOW CROPS FEED. The application of these principles to the question be- fore us is apparent. The young, active roots that are in contact with the soil are eminently hygroscopic, as is de- monstrated by the fact that they supply the plant with large quantities of water when the soil is so dry that it has no visible moisture. They therefore share with the soil the moisture which the latter contains. As water evaporates from the surface of the foliage, its place is supplied by the adjacent portions, and thus motion is es- tablished within the plant which propagates itself to the roots and through these to the soil. Each particle of water that flies off in vapor from the leaf makes room for the entrance of a particle at the root. If the soil and air have a surplus of water, the plant will contain more; if the soil and air be dry, it will contain less. Within certain narrow limits the supply and waste may vary without detriment to the plant, but when the loss goes on more rapidly than the supply can be kept up, or when the absolute content of water in the soil is re- duced toa certain point, the plant shortly wilts. Even then its content of water is many times greater than that of the soil. The living tobacco plant cannot contain less than 80°|, of water, while the soils in Sachs’ experiments contained but 12.3°|, and 1.5°|, respectively. When fully air-dry, vegetable matter retains 13°|, to 15°|, of water, while the soil similarly dry rarely contains more than 1-2°| .. The plant therefore, especially when living, is much more hygroscopic than the soil. If roots are so hygroscopic, why, it may be asked, do they not directly absorb vapor of water from the air of the soil? It cannot be denied that both the roots and fo- liage of plants are capable of this kind of absorption, and that it is taking place constantly in case of the roots. The experiments before described prove, however, that the higher orders of plants absorb very little in this way, THE FREE WATER OF THE SOIL. ILS too little, in fact, to be estimated by the methods hitherto employed. Sachs éxplains this as follows: Assuming that the roots have at a given temperature as strong an attrac- tion for water in the state of vapor as for liquid water, the amount of each taken up in a given time under the same circumstances would be in proportion to the weight of each contained in a given space. A cubic inch of water yields at 212° nearly a cubic foot (accurately, 1,696 times its volume, the barometer standing at 29.92 inches) of vapor. We may then assume that the absorption of liq- uid or hygroscopic water proceeds at least one thousand times more rapidly than that of vapor, a difference in rate that enables us to comprehend why a plant may gain water by its roots from the soil, when it would lose water by its roots were they simply stationed in air saturated with vapor. Again, the soil need not be more hygroscopic than roots, to supply the latter with water. It is important only that it present a sufficient surface. As is well known, a plant requires a great volume of earth to nourish it properly, and the root-surface is trifling, compared to the surface of the particles which compose the soil. Boussingault found by actual measurement that, accord- ing to the ‘rules of garden culture as practiced near Stras- burg, a dwarf bean had at its disposition 57 pounds of soil; a potato plant, 190 pounds; a tobacco plant, 470 pounds; and a hop plant, 2,900 pounds. These weights correspond to about 1, 3, '7, and 50 cubic feet respectively. The Quantity of Water in Vegetation is influenced by that of the Soil.—De Saussure observed that plants grow- ing in a dry lime soil contained less water than those from aloam. It is well known that the grass of a wet summer is taller and more succulent, and the green crop is heavier than that from the same field ina dry summer. It does not, however, make much more hay, its greater weight consisting to a large degree of water, which is lost in dry- 214 HOW CROPS FEED. ing. Ritthausen gives some data concerning two clover crops of the year 1854, from a loamy sand, portions of which were manured, one with ashes, others with gypsum. The following statement gives the produls of the nearly* fresh and of the air-dry crops. Weight in pounds per acre. --—H- ERRLIE ae canara. aa Fresh. Air-dry. Water lost in drying. Crop I, manured with ashes, 14,903° 5,182 9,721 ‘+ * unmanured, 12,380 5,418 6.962 Crop II, manured with gypsum, 22,256 4.800 17,456 “eS unmanured, 18,815 5,190 13,625 It is seen that while in both cases the fresh manured crop greatly outweighed the unmanured, the excess of weight consisted of water. In fact, the unmanured plots yielded more hay than the manured. The manured clover was darker in color than the other, and the stems were large and hollow, 1. e., by rapid growth the pith cells were broken away from each other and formed only a lining to the stalk, while in the unmanured clover the pith re- mained undisturbed, the stems being more compact in structure. (H.C. G., p. 369.) The Quantity of Soil-water most favorable to Crops has been studied by Hienkoff and Hellriegel. The former (Ann. der. Chem. u. Ph. 136, p. 160,) experimented with buckwheat plants stationed in pots filled with garden earth. The pots were of the same size and had the same — exposure at the south side of an apartment. The plants received at each watering in Pot No. 1, *|, liter of water 66 66 2, 1 |, 66 6é 14 66 3, 1 |, 74 3 14 ce 4, 1 |. 4 i 66 a 5 1 ie 66 * The clover was collected from the surface of a Saxon square ell, and was somewhat wilted before coming into Ritthausen’s hands. The quantities above given are calculated to English acres and pounds. THE FREE WATER OF THE SOIL. 215 The waterings were made simultaneously at the moment when all the water previously given to No. 1 was ab- sorbed by the soil. During the 67 days of the experi- ment the plants were watered 17 times. The subjoined table gives the results: Weight of | Weight of Fresh Crops in| dry Crops in| Number of Liters of No. of pot. grams. | grams. Seeds. water used. STRAW. | SEEDS. 1 27.99 4.52 1.68 til 25.0 2 65.05 8.47 5.47 283 125 3 24.95 4.55 1.73 93 6.25 4 9.98 1.41 0.52 37 3.12 5 2.30 0.30 0.09 12 1.56 The experiment demonstrates that the quantity of water supplied to a plant has a decided effect upon the yield. Pot No. 2 was most favorably situated in this re- spect. No. 1 hada surplus of water and the other pots received too little. 'The experiment does not teach what proportion of water in the soil was most advantageous, for neither the weight of the soil nor the size of the pot is mentioned. Hellriegel (Chem. Ackersmann, 1868, p. 15) experiment- ed with wheat, rye, and oats, in a pure sand mixed with a sufficiency of plant-food. The sand when saturated with water contained 25°|, of the liquid. ‘The following table gives further particulars of his experiments and the re- sults. ‘The weights are grams. WATER IN THE SOIL. |YIELD OF WHEAT.| YIELD OF RYE. YIELD OF OATS. In per cent| Straw Straw Straw In per centiof retentive) and and . and of Sot. power. Chaff. | Grain. | Chaff. | Grain. | Chaff. | Grain. 2144-5 10-20 7.0 2.8 8.3 3.9 4.2 1.8 5 -10 20-40 fost 8.4 11.8 8.1 11.8 7.8 10 -15 40-60 21.4 10.3 ptyaal 10.3 13.9 10.9 15 -20 60-80 23.3 11.4 16.4 10.3 15.8 11.8 In each ease the proportion of water in the soil was preserved within the limits given in the first column of the table, throughout the entire period of growth. It is seen that in this sandy soil 10-15 per cent of water ena- 216: HOW CROPS FEED. bled rye to yield a maximum of grain and brought wheat and oats very closely to a maximum crop. Hellriegel no- ticed that the plants exhibited no visible symptoms of deficiency of water, except. through stunted growth, in any of these experiments. Wilting never took place ex- cept when the supply of water was less than 2"|, per cent. Grouyen (Ueber den Zusammenhang zwischen Wit- terung, Boden und Diingung in ihrem Kinflusse auf die Quantitdt und Qualitat der Erndten, Glogau, 1868) gives the results of an extensive series of field trials, in which, among other circumstances, the influence of water upon the crops was observed. His discussion of the subject is too detailed to reproduce in this treatise, but the great influence of the supply of water (by rain, etc.,) is most strikingly brought out. The experimental fields were situated in various parts of Germany and Austria, and were cultivated with sugar beets in 1862, under the same fertilizing applications, as regards both kind and quantity. Of 14 trials in which records of the rain-fall were kept, the 8 best crops received from the time of sowing, May Ist, to that of harvesting, Oct. 15th, an average quantity of rain equal to 140 Paris lines in depth. The 6 poorest crops received in the same time on the average but 115 lines. During the most critical period of growth, viz., between the 20th of June and the 10th of September, the 8 best crops enjoyed an average rain-fall of 90.7 lines, while the 6 poorest received but 57.7 lines. It is a well recognized fact that next to temperature, the water supply is the most influential factor in the prod- uct of acrop. Poor soils give good crops in seasons of plentiful and well-distributed rain or when skillfully irri- gated, but insufficient moisture in the soil is an evil that no supplies of plant-food can neutralize. The Functions of Water in the Nourishment of Vegetation, so far as we know them, are of two kinds. THE FREE WATER OF THE SOIL. ps yf In the first place it is an unfailing and sufficient source of its elements,—hydrogen and oxygen,—and undoubtedly enters directly or indirectly into chemical combination with the carbon taken up from carbonic acid, to form sug- ar, starch, cellulose, and other carbohydrates. In the second place it performs important physical offices; is the vehicle or medium of all the circulation of matters in the plant; is directly concerned, it would appear, in imbibing gaseous food in the foliage and solid nutriment through the roots; and by the force with which it is absorbed, di- rectly influences the enlargement of the cells, and, per- haps, also the direction of their expansion,—an effect shown by the facts just adduced relative to the clover crops ex- amined by Ritthausen. Indirectly, also, water performs the most important ser- vice of continually solving and making accessible to crops the solid matters in the vicinity of their roots, as has been indicated in the chapter on the Origin of Soils. Combined Water of the Soil.—As already stated, there may exist in the soil compounds of which water is a chemi- cal component. True clay (kaolinite) and the zeolites, as well as the oxides of iron that result from weathering, con- tain chemically combined water. Hence a soil which has been totally deprived of its hygroscopic water by drying at 212°, may, and, unless consisting of pure sand, does, yield a further small amount of water by exposure to a higher heat. This combined water has no direct influence on the life of the plant or on the character of the soil, ex- cept so far as it is related to the properties of the com- pounds of which it is an ingredient. § 2. i THE AIR OF THE SOIL. 4 As to the free Oxygen and Nitrogen which exist in the interstices or adhere to the particles of the soil, there is 10 218 HOW CROPS FEED. little to add here to what has been remarked in previous paragraphs. Free Oxygen, as De Saussure and Traube have shown, is indispensable to growth, and must therefore be access- ible to the roots of plants. | The soil, being eminently porous, condenses oxygen. Blumtritt and Reichardt indeed found no considerable amount of condensed oxygen in most of the soils and sub- stances they examined (p. 167); but the experiments of Stenhouse (p. 169) and the well-known deodorizing effects of the soil upon fecal matters, leave no doubt as to the fact. The condensed oxygen must usually spend itself in chemical action. Its proportion would appear not to be large; but, being replaced as rapidly as it enters into com- bination, the total quantity absorbed may be considera- ble. Organic matters and lower oxides are thereby ox- idized. Carbon is converted into carbonic acid, hydrogen into water, protoxide of iron into peroxide. The upper portions of the soil are constantly suffering change by the action of free oxygen, so long as any oxidable matters exist in them. These oxidations act to solve the soil and render its elements available to vegetation. (See p. 131.) Free Nitrogen in the air of the soil is doubtless indiffer- ent to vegetation. The question of its conversion into — nitric acid or ammonia will be noticed presently. (See p. 259.) Carbonic Acid.—The air of the soil is usually richer in carbonic acid, and poorer in oxygen, than the normal at- mosphere, 'while the proportion (by volume) of nitrogen is the same or very nearly so. The proportions of car- bonic acid by weight in the air included in a variety of soils have already been stated. Here follow the total quantities of this gas and of air, as well as the composi- tion of the latter in 100 parts by volume, as determined by THE AIR OF THE SOIL. a 219 Boussingault and Lewy. (Mémoires de Chimie Agricole, étc., p. 369.) Ee [S> Ss iss ef iss s§ (SS 2 cs . So S ae S'S | Composition. of the SS |, 2 3 lair in the soil %n 100 3s & Sx | parts by volume, Q S iy - a ae Ss |S=8 | tonic Aas Nitro SS Sel ace (IS |: Be Bandy subsoil: of. forest. .i6.56.006is eet en 4416} 14 | 0.24 Loamy ‘“ SR, ei he da 3' youn oh caretnainiota aes 3530) 28 | 0.79 | 19.66) 79.55 PEAS BOT ee PI ois ee atate ate weleles See 5891} . 57 | Ox87 | 19.61] 79.52 iiayey, ~~ of artichoke field .............-.-: 10310) 71 | 0.66 | 19.99) 79.35 Soil of asparagus bed not manured for one year| 11182) 86 | 0.74 | 19.02) 80.24 ahs = “newly manured....<...5. 11182} 172 | 1.54 | 18.80) 79.66 Sandy soil, six days after manuring....[of rain) 11783) 257 | 2.21 iy ao ik os three days} 11783) 11 9.74 | 10.35) 79.91 Vegetable mold-compost............csceeeceee 21049) _%72 | 3.64 | 16.45] 79.91 28 [Ss S18 SS lok % Sie See osu Se = Ss SoS ss 8 Sx 0 int OF ad y= ¢ ‘composition of aér tai Sh aove the soil 2n 100 Se See arts. e* 8.5 — S~ 12 sa| Car- BAe SE Se | Donte | een. | gen, SS iSsS | aca. | YI | IM / { or S io?) ) oO 12 | 0.025)20.945|'79 .030 The percentage, as well as the absolute quantity of car- bonic acid, is seen to stand in close relation with the or- ganic matters of the soil. The influence of the recent application of manure rich in organic substances is strik- ingly shown in case of the asparagus bed and the sandy soil. The lowest percentage of carbonic acid is 10 times that of the atmosphere a few feet above the surface of the earth, as determined at the same time, while the highest percentage is 390 times that proportion. Even in the sandy subsoil the quantity of free carbonic acid is as great as in an equal bulk of the atmosphere ; and in the cultivated soils it is present in from 6 to 95 220 HOW CROPS FEED. times greater amount. In other words, in the cultivated soils taken to the depth of 14 inches, there was found as much carbonic acid gas as existed in the same horizontal. area of the atmosphere through a height of 7 to 110 feet. The accumulation of such a percentage of carbonic acid gas in the interstices of the soil demonstrates the rapid formation of this substance, which must as rapidly diffuse - off into the air. The roots, and, what is of more signifi- cance, the leaves of crops, are thus far more copiously fed with this substance than were they simply bathed by the free atmosphere so long as the latter is unagitated. When the wind blows, the carbonic acid of the soil is | of less account in feeding vegetation compared with that ‘of the atmosphere. When the air moves at the rate of two feet per second, the current is just plainly perceptible. A mass of foliage 2 feet high and 200 feet* long, situated in such a current, would be swept by a volume of atmos- phere, amounting in one minute to 48,000 cubic feet, and containing 12 cubic feet of carbonic acid. In one hour it would amount to 2,280,000 cubic feet of air, equal to 720 cubic feet of carbonic acid, and in one day to 69,120,000 cubic feet of air, containing no less than 17,280 cubic feet of carbonic acid. | In a brisk wind, ten times the above quantities of air and carbonic acid would pass by or through the foliage. It is plain, then, that the atmosphere, which is rarely at rest, can supply carbonic acid abundantly to foliage with- out the concourse of the soil. At the same time it should not be forgotten that the carbonic acid of the atmosphere is largely derived from the soil. Carbonic Acid in the Water of the Soil.—Notwith- standing the presence of so much carbonic acid in the air of the soil, it appears that the capillary soil-water, or so * A square field containing one acre is 208 feet and a few inches on each side. THE AIR OF THE SOIL. 231 ~ much of it as may be expressed by pressure, is not nearly saturated with this gas. De Saussure (Recherches Chimiques sur la Végétation, p- 168) filled large vessels with soils rich in organic mat- ters, poured on as much water as the earth could imbibe, allowing the excess to drain off and the vessels to stand five days. Then the soils were subjected to powerful pressure, and the water thus extracted was examined for carbonic acid. It contained but 2°|, of its volume of the gas. Since at a medium temperature (60° F’.) water is capa- ble of dissolving 100°|, (its own bulk) of carbonic acid, it would appear on first thought inexplicable that the soil- water should hold but 2 percent. Henry and Dalton long ago demonstrated that the relative proportion in which the ingredients of a gaseous mixture are absorbed by wa- ter depends not only on the relative solubility of each gas by itself, but also on the proportions in which they exist in the mixture. The large quantities of oxygen, and - especially of nitrogen, associated with carbonic acid in the pores of the soil, thus act to prevent the last-named gas being taken up in greater amount; for, while carbonie acid is about fifty times more soluble than the atmos- pheric mixture of oxygen and nitrogen, the latter is pres- ent in fifty times (more or less) the quantity of the former. Absorption of Carbonic Acid by the Soil. According to Van den Broek, (Ann. der Chemie u. Ph., 115, p. 87) certain wells in the vicinity of-Utrecht, Holland, which are exca- vated only a few feet deep in the soil of gardens, contain water which is destitute of carbonic acid (gives no precipi- tate with lime-water), while those which penetrate into the underlying sand contain large quantities of carbonate of lime in solution in carbonic acid. Van den Broek made the following experiments with garden-soil newly manured, and containing free carbonic acid in its-interstices, which could be displaced by a cur- 922 HOW CROPS FEED. rent of air. Through a mass of this earth 20 inches deep and 3 inches in diameter, pure distilled water (free from carbonic acid) was allowed to filter. Jt ran through without taking up any of the gas. Again, water contain- ing its own volume of carbonic acid was filtered’ through a similar body of the same earth. This water gave up all its carbonic acid while in contact with the soil. After a certain amount had run off, however, the subsequent por- tions contained it. In other words, the soils experiment- ed with were able to absorb carbonic acid from its aqueous solution, even when their interstices contained the gas in the free state. These extraordinary phenomena deserve further study. Be NON-NITROGENOUS ORGANIC MATTERS OF THE SOIL.— CARBOHYDRATES. VEGETABLE ACIDS. VOLATILE ORGANIC ACIDS. HUMUS. Carbohydrates, or Bodies of the Cellulose Group.— The steps by which organic matters become incorporated with the soil have been recounted on p. 135. When plants perish, their proximate principles become mixed with the soil. ‘These organic matters shortly begin to decay or to pass into humus. In most circumstances, however, the soil must contain, temporarily or periodically, unalter- ed carbohydrates. Cellulose, especially, may be often found in an unaltered state in the form of fragments of straw, etc. De Saussure (Recherches, p. 174) found that water dis- solved from a rich garden soil that had been highly ma- nured for a long time, several thousandths of organic matter, giving an extract, which, when concentrated, had an almost syrupy consistence and a*sweet taste, was neither acid nor alkaline in reaction, and comported itself not unlike an impure mixture of glucose and dextrin. ORGANIC MATTERS OF THE SOIL. 223 Verdeil and Risler have made similar observations on ten soils from the farm of the Institut Agronomique, at Ver- sailles. They found that the water-extract of these soils contained, on the average, 50°|, of organic matter, which, when strongly heated, gave an odor like burning paper or sugar. These observers make no mention of crenates or apocrenates, and it, perhaps, remains somewhat doubtful, therefore, whether their researches really demonstrate the presence in the soil of a neutral body identical with, or allied to, dextrin or sugar. Cellulose, starch, and dextrin, pass by fermentation into sugar (glucose); this may be resolved into lactic acid (the acid of sour milk and sour-krout), butyric acid (one of the acids of rancid butter), and acetic acid (the acid of vine- gar). It must often happen that the bodies of the cellu- lose group ferment in the soil, the same as in the souring of milk or of dough, though they suffer for the most part conversion into humus, as will be shortly noticed. Vegetable Acids, viz., oxalic, malic, tartaric, and citric acids, become ingredients of the soil when vegetable mat- ters are buried in it. When the leaves of beets, tobacco, and other large-leaved plants fall upon the soil, oxalic and malic acids may pass into it in considerable quantity. Falling fruits may give it citric, malic, and tartaric acids, These acids, however, speedily suffer chemical change when in contact with decaying albuminoids. Buchner has shown (Ann. Ch. u. Ph., 78, 207) that the solutions of salts of the above-named vegetable acids are rapidly con- verted into carbonates when mixed with vegetable fer- ments. In this process tartaric and citric acids are first partially converted into acetic acid, and this subsequently passes into carbonic acid. Volatile Organic Acids,—Formic, propionic, acetic, and butyric acids, or rather their salts, have been detected by Jongbloed and others in garden earth, They are common 224 HOW CROPS FEED. products of fermentation, a process that goes on in the juices of plants that have become a part of the soil or of a compost. These acids can scarcely exist in the soil, except tempo- rarily, as results of fermentation or decay, and then in but very minute quantity. They consist of carbon, hydrogen, and oxygen. Their salts are all freely soluble in water. Their relations to agricultural plants have not been studied. Hummus (in part).—The general nature and origin of humus has been already considered. It is the débris of vegetation (or of animal matters) in certain stages of de- composition. Humus is considerably complex in its chemical character, and our knowledge of it is confessedly incomplete. In the paragraphs that immediately follow, we shall give from the best sources an account of its non- nitrogenous ingredients, so far they are understood, resery- ing toa later chapter an account of its nitrogenized con- stituents. The Non-nitregenous Components of Humus.—The appearance and composition of humus is different, accord- ing to the circumstances of its formation. It has already been mentioned that humus is brown or black in color. It appears that the first stage of decomposition yields the brown humus. It is seen in the dead leaves hanging to a tree In autumn, in the upper layers of fallen leaves, in the outer bark of trees, in the smut of wheat, and in the up- per, dryer portions of peat. When brown humus remains wet and with imperfect access of air, it decomposes further, and in time is convert- ed into black humus. Black humus is invariably found in the soil beyond a little depth especially if it be com- pact, in the deeper layers of peat, in the interior of com-. post heaps, in the lower portions of the leaf-mould of forests, and in the mud or muck of swamps and ponds, Ulmic Acid and Uilmin.—The brown humus contains ORGANIC MATTERS OF THE SOIL. 295 (besides, perhaps, unaltered vegetable matters) two char- acteristic ingredients, which have been designated ulmic acid and wlmin, (so named from having been found in a brown mass that exuded from an elm tree, wmus being the Latin for elm). These two bodies demand particular notice. When brown peat is boiled with water, it gives a yel- lowish. or pale-brown liquid, being but little soluble in pure water. If, however, it be boiled with dilute solution of carbonate of soda (sal-soda), a dark-brown liquid is obtained, which owes its color to ulmate of soda. The alkali dissolves the insoluble ulmic acid by combining with it to form a soluble compound. By repeatedly heat- ing the same portion of peat with new quantities of sal- soda solution, and pouring off the liquids each time, there arrives a moment when the peat no longer yields any color to the solution. The brown peat is thus separated into one portion soluble, and another insoluble, in carbonate of soda. Ulmic acid has passed into the solution, and ulmin* remains undissolved (mixed, it may be, with unaltered vegetable matters, recognizable by their form and. struc- ture, and with sand and mineral substances). By adding hydrochloric acid to the brown solution as long as it foams or effervesces, the ulmic acid separates in brown, bulky flocks, and is insoluble in dilute hydrochloric acid, but is a little soluble in pure water. When moist, it has an acid reaction, and dissolves readily in alkalies or alkali-carbonates. On drying, the ulmic acid sbrinks greatly and remains as a brown, coherent mass. The ulmin* which remains after treatment of brown peat with carbonate of soda is an indifferent, neutral (i. e., not acid) body, which has the same composition as the * The above statement is made on the authority of Mulder. The writer has, however, found, in several cases, that continued treatment with carbonate of soda alone completely dissolves the humus, leaving a residue of cellulose which yields nothing to caustic alkali. He is, therefore, inclined to disbelieve in the existence of ulmin and humin as distinct from ulmic and humic acids. 226 HOW CROPS FEED. ulmic acid. By boiling it with caustic soda or potash-lye, it is converted without change of composition into ulmie acid. On gently heating sugar with dilute hydrochlorie acid, a brown substance is produced, which appears to be iden- tical with the ulmic acid obtained from peat. Humic Acid and Humin, — By treating black humus with carbonate of soda as above described, it is separated’ into humic acid and humin*, which closely resemble ulmic acid and ulmin in all their properties—possess, however, a black color, and, as it appears, a somewhat different com- position. Humic acid and humin may be obtained also by the action of hot and strong hydrochloric acid, of sulphuric acid, and of alkalies, upon sugar and the other members of the cellulose group. Composition of Ulmin, Ulmic Acid, Humin, and Humic Acid,—The results of the analyses of these bodies, as ob- tained by different experimenters and from different sources, are not in all cases accordant. Either several dis- tinct substances have been confounded under each of the above names, or the true ulmin and humin, and ulmic and humic acids, are liable to occur mixed with other matters, from which they cannot be or have not been perfectly separated. Mulder (Chemie der Ackerkrume, 1, p. 322), who has chiefly investigated these substances, believes there is a group of bodies having in general the characters of ulmin and ulmic acid, whose composition differs only by the ele- ments of water,t and is exhibited by the general formula C,, H,, OC; - nH,0, in which nH,0O signifies one, two, three, or more of water. * See note on page 225. + In a way analogous to what is known of the sugars. (H.C. G., p. 80.) / ORGANIC MATTERS OF THE SOIL. Ze Ulmic acid from sugar has the following composition in 100 parts ; Carbon, 67.1 Hydrogen, 4.2 Oxygen, 28.7 100.0 which corresponds to C,, H,, O,, H,O. Mulder considers that in ‘the same manner there exist various kinds of humic acids and humin, differing from each other by the elements of water, all of which may be represented by the general formula C,, H,, O,, nH,O. Humie acid and humin from sugar, corresponding to C,, H,, O,, + 3H,O, have, according to Mulder, the fol- lowing composition per cent: Carbon, 64 Hydrogen, 4 Oxygen, — 32 100 Apocrenic and Crenic Acids.—In the acid liquid from which ulmic or humic acid has been separated, exist two other acids which were first discovered by Berzelius in the Porla spring in Sweden, and which bear the names apocrenic acid and crenic acid respectively. By adding soda to the acid liquid until the hydrochloric acid is neu- tralized, then acetic acid in slight excess, and lastly solu- tion of acetate of copper (crystallized verdigris) as long as a dirty-gray precipitate is formed, the apocrenic acid is procured in combination with copper and ammonia. From this salt the acid itself may be separated* as a brown, gummy mass, which is easily soluble in water. Accord- ing to Mulder it has the formula C,, H,, O,, + H,O, or, in 100 parts, * By precipitating the copper with sulphuretted hydrogen. 228 HOW CROPS FEED. Carbon, 56.47 Hydrogen, 2.75 Oxygen, 40.78 100.00 Crenate of copper is lastly precipitated as a grass-green substance by adding acetate of copper to the liquid from which the apocrenate of copper was separated, and then neutralizing the free acid with ammonia. From this com- pound crenic acid may be prepared as a white, solid body of sour taste, to which Mulder ascribes the formula C,, H,, O,, + 38H,O, and in 100 parts the following compo- sition ° Carbon, 45.70 Hydrogen, 4.80 Oxygen, 49.50 100.00 Mutual Conversion of Apocrenic and Crenic Acids, —When, on the one hand, apocrenic acid is placed in - contact with zine and dilute sulphuric acid, the hydrogen evolved from the latter converts the brown apocrenic acid (by uniting with a portion of its oxygen) into colorless crenic acid. On the other hand, the solution of crenic acid exposed to the air shortly becomes brown by absorp-— tion of oxygen and formation of apocrenic acid. These changes may be repeated many times with the same por- tion of these substances. Mulder remarks (Chemie der Ackerkrume, p. 350): “In every fertile soil these acids always occur together in not inconsiderable quantities. When the earth is turned over by the plow, two essentially different processes fol- low each other: oxidation, where the air has free access ; reduction, where its access is more or less limited by the adhesion of the particles and especially by moisture. In the loose, dry earth apocrenic acid is formed; in the firm, ORGANIC MATTERS OF THE SOIL. 229 moist soil, and in every soil after rain, crenic acid is pro- duced, so that the action or effects of these substances are alternately manifested.” The Humus Bodies Artificially Produced. — When sugar, cellulose, starch, or gum, is boiled with strong hy- drochloric acid or a strong solution of potash, brown or black bodies result which have the greatest similarity with the ulmin and humin, the ulmic and humic acids of peat and of soils. By heating humus with nitric acid (a vigorous oxidizing agent), crenic and apocrenic acids are formed. The pro- duction of these bodies by such artificial means gives in- teresting confirmation of the reality of their existence, and demonstrates the correctness of the views which have _ been advanced as to their origin. While the precise composition of all these substances may well be a matter of doubt, and from the difficulties of obtaining them in the pure state is likely to remain so, their existence in the soil and their importance in agricul- tural science are beyond question, as we shall shortly have opportunity to understand. The Condition of these Humus Bodies in the Soil requires some comment. The organic substances thus noticed as existing in the soil are for the most part acids, but they do not exist to much extent in the free state, ex- cept in bogs and morasses. SS © | SSES SaaS = S a) —— = A> S Set ERS ie So sage S: Ss [te Pee (Sse ia esis sa S — Ss MSR Rg eon, al eae Se S 7 Sy Ss 8 S°S+ | SSe | SS. 8 |S SSe2 = *. 38 Ss cS SS Sos | Ss$ss [8,. Ses Bil. as BS BS | R83 | RSs [SESS ISSSRS | grms. | grms. | grms. | grms. | grms. | grms. | grms. grms. —; ———_——————|--—.c00an ——— ee 1..| 0.0033 | 0.0000 | 0.0033 } 0.0053 | 0.0020+ | 0.397 1 1 2..| 0.0033 | 0.0033 | 0.0066 | 0.0063 | 0.0002¢ | 0.720 | 1.8 2 a 0.0033 0.0066 | 0.0099 | 0.0097 | 0.0002 1.130 2.8 3 4..| 0.0033 0.0264 | 0.0297 0.0251 | 0.0046 3.280 8.5 9 * N=Nitrogen. In the first Exp. a trifling quantity of nitrogen was gathered (as ammonia?) from the air. In the others, and especially in the last, nitrate of soda remained in the soil, 12% . 274 , HOW CROPS FEED. not having been absorbed entirely by the plants. Observe, however, what a remarkable coincidence exists between the ratios of supply of nitrogen in form of a nitrate and those of growth of the several crops, as exhibited in the last two columns of the Table. Nothing could, demon- strate more strikingly the nutritive function of nitric acid than these admirable investigations. Of the multitude of experiments on vegetable nutrition , which have been recently made by the process of water- culture (ZZ. C. G., p. 167), nearly all have depended upon nitric acid as the exclusive source of nitrogen, and it has proved in all cases not only adequate to this purpose, but far more certain in its effects than ammonia or any other nitrogenous compound. § 6. NITROGENOUS ORGANIC MATTERS OF THE SOIL. AVAILABLE NITROGEN.—QUANTITY OF NITROGEN REQUIRED FOR CROPS. In the minerals and rocks of the earth’s surface nitrogen is a very small, scarcely appreciable ingredient. So far as we now know, ammonia-salts and nitrates (nitrites) are the only mineral compounds of nitrogen found in soils. When, however, organic matters are altered to humus, and become a part of the soil, its content of nitrogen ac- quires significance. In peat, which is humus compara- tively free from earthy matters, the proportion of nitrogen is often very considerable. In 82 specimens of peat ex- amined by the author (Peat and tis Uses as Fertilizer and Fuel, p. 90), the nitrogen, calculated on the organic mat- ters, ranged from 1.12 to 4.31 per cent, the average being 2.6 per cent. The average amount of nitrogen in the air- dry and in some cases highly impure peat, was 1.4 per cent. This nitrogen belongs to the organic matters in NITROGENOUS ORGANIC MATTERS OF THE SOIL. 275 great part, but a small proportion of it being in the form of ammonia-salts or nitrates. In 1846, Krocker, in Liebig’s laboratory, first estimated the nitrogen in a number of soils and marls (An. Ch. u. Ph., 58, 387). Ten soils, which were of a clayey or loamy character, yielded from 0.11 to 0.14 per cent; three sands gave from 0.025 to 0.074 per cent; seven marls contained 0.004 to 0.083 per cent. Numerous examinations have since been made by An- derson, Liebig, Ritthausen, Wolff, and others, with simi- lar results. In all but his latest writings, Liebig has regarded this nitrogen as available to vegetation, and in fact designated it as ammonia. Way, Wolff, and others, have made evi- dent that a large portion of it exists in organic combina- tion. Boussingault (Agronomie, T. I) has investigated the subject most fully, and has shown that in rich and - highly manured soils nitrogen accumulates in considerable quantity, but exists for the most part in an insoluble and inert form. In the garden of Liebfrauenberg, which had been heavily manured for centuries, but 4°], of the total nitrogen existed as ammonia-salts and nitrates. The soil itself contained— — Total nitrogen, 0.261 per cent. Ammonia, GrOOZBur Fo LS Nitric acid, _ 0.00034 “ bis The subjoined Table includes the results of Boussin- gault’s examinations of a number of soils from France and South America, in which are given the quantities of am- monia, of nitric acid, expressed as nitrate of potash, and of nitrogen in organic combination. These quantities are stated both in per cent of the air-dry soil, and in lbs. av. per acre, taken to the depth of 17 inches. In another column is also given the ratio of nitrogen to carbon in the organic matters. (Agronomie, T I, pp. 14-21.) 276 HOW CROPS FEED, AmmMontrdé, NITRATES, .ND OrGANIC NITROGEN OF VAnRrIouUS SOILS. : Nitrate of || Nitrogen in |-s Ammonia. potash. org. combi n. ay a ° — —_— e o~ . Soils. : Ibs. |]. ‘{Ibs. Ibs [oss per |per|| per |per|| per | per [SR cent. jacre|| cent |acre!| cent. | acre |I@S 8 o { Liebfrauenberg, '§ [Liebfrauenberg, light gard. soil soil |0.0022 100) |0.0175*| 875)| 0.259) 12970} 1:9.3 ¢ J Bischwiller, light garden soil... /0.0020) 100)|0.1526 |%630}| 0.295] 14755] 1:9.7 3 Bechelbronn, wheat field clay. 0.0009} 45//0.0015 | || 0.189) 6985] 1:8.2 —, |Argentan, rich pastures. 20.5 0.0060] 300)|0.0046 | 230)) 0.518] 25650) 1:8 ¢ {Rio Madeira, sugar field, clay|0.0090| 450)|0.0004 | 20/| 0.143} "7140! 1:6.3 = | {Rio Trombetto forest heavy do. |0.00380} 183) |0.0001 5|}} 0.119} 5955) 1:4.9 z | Rio Negro, prairie v. fine sand. |0.003S} 190/|0.0001 5|| 0.068) 3440) 1:5.6 =| } Santarem, cocoa plantation.. |0.0088} 415//0.0011 | 55/| 0.649} 82450) 1:11 eee etc. SSS S§| §8§| S81 8 $ |ESS! sls 8 S58 S8/ 38] S83) 85] 8 [S83] 8 [Ss SPs] 8 | S51 S45] SN) SS] S 125! Sissel eS RSS] SPaAds Ss As SS] SY Sse] B [Rel & Mall ...[Walk]! 43.00/57.00/48.92/25.60] 4.27] 1 55| 0.62; 7.63) 5.49/38.77) -— Pheasant %0.50/29.90/31.49)35.29) 2.16] 0.47|trace 3.55|13.67/4.93)| — Worl. ose e.'s 35.00/65 .00|48.45] 6.08] 2.75] 1.21) — 6.19)25.%1/5.06) — Queen's Ave..} 44.00/56.00)43.%5] 6.08) 6.32} 2.00|trace | 14.45|15.61/4.13| — itchen Gard.| $7.00/63.00/26.60/12.35/11.20/trace |trace | 18.51|19.60]'7.23/trace Satory..[Galy! 83.00167.00/18.70)24.25/18.50| 3.72] 0.50} — |21.60/4.65}) — Clay soil of | 48.00/52.00/18.75/45.61] 3.83} 0.95} 1.55] 9.14! 5.00)7.60] '7.60 Lime soil, do.} 47.00/53.00/17.21/48.50} 9.00;trace | — 6.21] 5.50) — | 8.32 Peat bog..... 46 .00|54.00/24.43/30.61} 0.92] 5.15/trace 6.06) 8.%5/7.45) — Sand pit..... 47 .04/52.06/22.31134.59! 8.10) 1.02) — 4.05/15.58/6.47], — Here we notice that in almost every instance all the mineral ingredients of the plant were extracted from these soils by water. Only magnesia and chlorine are in any case missing. We are not informed, unfortunately, what amount of soluble matters was obtained in these experiments. We next adduce a number of statements of the pro- portion of matters which water is capable of extracting from earth, statements derived from the analyses of soils of widely differing character and origin. | I. Very rich soil (excellent for clover) from St. Martin’s, Upper Austria, treated with six times its quantity of cold water (Jarriges). II. Excellent beet soil (but clover sick) from Schlan- staedt, Silesia, treated with 5 times its quantity of cold water (Jarriges). III. Fair wheat soil, Seitendorf, Silesia, treated with 5 times its weight of cold water (Peters). IV. Inferior wheat soil from Lampersdorf, Silesia— 5-fold quantity of water (Peters). | V. Good wheat soil, Warwickshire, Scotland—10-fold quantity of hot water (Anderson). . VI. Garden soil, Cologne—3-fold amount of cold wate (Grouven). . AQUEOUS SOLUTION OF THE SOIL. Sis VII. Garden soil, Heidelberg —3-fold amount of cold water (Grouven). VIII. Poor, sandy soil, Bickendorf—3-fold amount of cold water (Grouven). IX. Clay soil, beet field, Liebesnitz, Bohemia, extract- ed with 9.6 times its weight of water (R. Hoffmann). X. Peat, Meronitz, Bohemia, extracted with 16 times its weight of water (R. Hoffmann). XI. Peaty soil of meadow, extracted with 8 times its weight of water (R. Hoffmann). XII. Sandy soil, Moldau Valley, Bohemia, treated with twice its weight of water (R. Hoffmann). XI. Salt meadow, Stollhammer, Oldenburg (Harms). XIV. Excellent beet soil, Magdeburg (Hellriegel). XV. Poor beet soil, but good grain soil, Magdeburg (Hellriegel). | XVI. Experimental soil, Ida-Marienhiitte, Silesia, treat- ed with 24 times its weight of cold water (Kiillenberg). XVII. Soil from farm of Dr. Geo, B. Loring, Salem, Mass., treated with twice its weight of water (W. G. _ Mixter). MATTERS DISSOLVED BY WATER FROM 100,000 PARTS OF VARIOUS SOILS. 38 ' E Q = - |S /s| sg | 88] & | Ss] & SeS/lS8] & Sie |s| 8 |s2| = -s8| 8 Bessel S ; NN S 1h] Q@lis ; 5 e&! 08 8 2k, ae Ea <3 S * * —~ S , 8 ‘S&S 4 S§ 8S 63. oem Barley Grain, 43.75 81 42 81° - 12 08> 1439 oe 20° 4.6. - 3.0. Ne 6.0 28° | 262 a Straw, 100.00 1 | | | | Total, 143.75 2201 63 61 85 22 204 40° 81 In the account of Hellriegel’s experiments, it is stated — | that the maximum barley crop in some other of his trials, _ corresponds to 8,160 lbs. of grain, or 154 bushels of 53 _ Ibs. each per acre. This is more than 44 times the yield above assumed. The above figures show that no éssential ash-ingredi- — ent of the oat crop is present in larger quantity than potash. Phosphoric acid is quite the same in amount, * These figures are employed by Anderson, and are based on Scotch statistics. REVIEW AND CONCLUSION. 365 while lime is but one-half as much, and the other acids and bases are still less abundant. It follows then that if 71 lbs. of available potash in 1,000.000 of soil are enough for a barley crop 4} times greater than can ordinarily be produced under agricultural conditions, the same quantity of phosphoric acid, and less than half that amount of lime, etc., must be ample. Calculating on this basis, we give in the following statement the quantities required per acre, taken to the depth of one foot, to produce the max- imum crop of Hellricgel (1), and the quantities needed for the average crop of 33 bushels (2). The amounts of nitrogen are those which Hellriegel found adequate to the wheat crop. See p. 289, i 2 lbs lbs. Potash, 248 55 Soda, 78 17 Magnesia, %6 17 Lime, 105 28 Phosphoric acid, 230 55 Sulphuric acid, 49 11 Chlorine, 38 8 Nitrogen, 245 54 If now we divide the total quantities of potash, etc., found in an acre, or 3,500.000 lbs. of the soil analyzed by Baumhauer, by the number of pounds thus estimated to be necessarily present in order to produce a maximum or an average yield, we have the following quotients, which give the numberof maximum barley crops and the number of average crops, for which the soil can furnish the re- spective materials. The Zuider Zee soil contains enough Lime for 1364 maximum and 6138 average barley crops. Potash 66 144 66 &“ 648 “cc a4 “cc Phosphoric acid “665 “ “ 9993 “ rT Sulphuric 6 a 64 rT “ 99g & « ry Nitrogen in ammonia “ v4 ot 6 31.“ “ “ We give next the composition of one of the excellent 366 _ HOW CROPS FEED. wheat soils of Mid Lothian, analyzed by Dr. Anderson. The air-dry surface-soil contained in 100 parts: BUCA y. . ce oe cles coe wees cleie'y cs sats Sale ene een 71.552 Aaa. soe ie ats eateries a + 0 d-)ssage ints A » 6.935 Peroxide OF FFOD >. S.526 «acs ¥ dcx ssa. eee 5.178 Maonesias iii; sjiisic So tine caidels s cosas Bae ee 1 082 POPE Ass he aae ecwienbiotnesteeeiesa tne 0.354 SION yo civ: p-s hosbfaievaie'e 0b a'e,2 piainie sie Sin’ weela ee oe eee 0.483 POPEPPIRTLPIC CICS oc a sis ce mie.e oe Sele wise bas atte ie eee 0.044 Phosphorit acid 2'. 2200°.3.20. Acs oe Soe 0.480 CHIOTINeG Wi sid. bad ies pe babs sensei eae ee traces Organic matter. a... 33s. 5 5.26 See 2 eee ees Mer trace AMikaliesi vs..én csc sid (hissed eT ene ae none Quartz and insoluble ‘silicates... <<... csjst¥ sen = 0) = 95.863 100.000 Here we note the absence in weighable quantity of: magnesia and phosphoric acid, while potash could not even REVIEW AND CONCLUSION. 367 be detected by the tests employed. This soil was mostly naked and destitute of vegetation, and its composition shows the absence of any crop-producing power. Relative Importance of the Ingredients of the Soil. —From the general point of view of vegetable nutrition, all those ingredients of the soil which act as food to the plant, are equally important as they are equally indispens- able. Absence of any one of the substances which water- culture demonstrates must be presented to the roots of a plant so that it shall grow, is fatal to the productiveness: of a soil. Thus regarded, oxide of iron is as important as phos- phoric acid, and chlorine (for the crops which require it). is no less valuable than potash. Practically, however, the relative importance of the nutritive elements is meas- ured by their comparative abundance. Those which, like oxide of iron, are rarely deficient, are for that reason less prominent among the factors of a crop. If any single substance, be it phosphoric acid, or sulphuric acid, or pot- ash, or magnesia, is lacking in a given soil at a certain time, that substance is then and for that soil the most im- portant ingredient. From the point of view of natural abundance, we may safely state that, on the whole, availa- ble nitrogen and phosphoric acid are the most important ingredients of the soil, and potash, perhaps, takes the next rank, These are, most commonly, the substances whose absence or deficiency impairs fertility, and are those which, when added as fertilizers, produce the most frequent and remarkable increase of productiveness. In a multi- tude of special cases, however, sulphuric acid or lime, or magnesia, assumes the chief prominence, while in many in- stances it is scarcely possible to make out a greater crop- producing value for one of these substances over several others. Again, those ingredients of the soil which could be spared for all that they immediately contribute to the 368 HOW CROPS FEED. nourishment of crops, are often the chief factors of fer- tility on account of their indirect action, or because they supply some necessary physical conditions. Thus humus is not in any way essential to the growth of agricultural plants, for plants have been raised to full perfection with- out it; yet in the soil it has immense value practically, since among other reasons it stores and supplies water and assimilable nitrogen. Again, gravel may not be in any sense nutritious, yet because it acts as a reservoir of heat and promotes drainage it may be one of the most import- ant components of a soil. What the Soil must Supply.—It is not sufficient that the soil contain an adequate amount of the several ash-in- gredients of the plant and of nitrogen, but it must be able to give these over to the plant in due quantity and pro- portion. The chemist could without difficulty compound an artificial soil that should include every element of plant-food in abundance, and yet be perfectly sterile. The potash of feldspar, the phobpheas acid of massive apatite, the nitrogen of peat, are nearly innutritious for crops on account of their immobility—because they are locked up in insoluble combinations, Indications of Chemical Analysis.—The analyses by Baumhauer of soils from the Zuider Zee, p. 362, give in a single statement their ultimate composition. We are in- formed how much phosphoric acid, potash, magnesia, etc., exist in the soil, but get from the analysis no clue to the amount of any of these substances which is at the dispo- sition of the present crop. Experience demonstrates the productiveness of the soil, and experience also shows that a soil of such composition is fertile; but the analysis does not necessarily give proof of the fact. A nearer approach to providing the data for estimating what a soil may sup- ply to crops, is made by ascertaining what it will yield to acids, REVIEW AND CONCLUSION. 369 Boussingault has analyzed in this manner a soil from Calvario, near Tacunga, in Equador, South America, which possesses extraordinary fertility. He found its composition to be as follows: Nitrogen in organic combination, 0.243 Nitric acid, 0.975 Ammonia, 0.010 Phosphoric acid, 7 0.460 Chlorine, 0.395 Sulphuric acid, 0.023 Carbonie acid 3 : traces Po ionand soda: rSoluble in acids. 1.030 Lime, 1.256 Magnesia, 0.875 Sesquioxide of iron, 2.450 Sand, fragments of pumice, and clay insoluble in acids, 83.195 Moisture, 3.150 Organic matters (less nitrogen), undetermined substances, and loss, 5.938 100.000 This analysis is much more complete in reference to ni- trogen and its compounds, than those by Baumhauer al- ready given (p. 362), and therefore has a peculiar value. As regards the other ingredients, we observe that phos- phoric acid is present in about the same proportion; lime, alkalies, sulphuric acid, and chlorine, are less abundant, while magnesia is more abundant than in the soils from Zuider Zee. | The method of analysis is a guarantee that the one per cent of potash and soda does not exist in the insoluble form of feldspar. Boussingault found fragments of pumice by a microscopic examination. This rock is vesicular feld- spar, or has at least a composition similar to eae: and the same insolubility in acids. The inert nitrogen of the humus is discriminated from that which in the state of nitric acid is doubtless all assim- ilable, and that which, as ammonia, is probably so for the most part. The comparative solubility of the two per cent of lime and magnesia is also indicated by the analysis. 16* ‘370 - . HOW CROPS FEED. Boussingault does not state the kind or concentration, or temperature of the acid employed to extract the soil for the above analysis. ‘These are by no means points of indifference. .Grouven (lter & 3ter Salzmiinder Berichte) — has extracted the same earth with hydrochloric acid, con- centrated and dilute, hot and cold, with greatly different — results as was to be anticipated. In 1862, a sample from — an experimental field at Salzmiinde was treated, after be- — ing heated to redness, with boiling concentrated acid for — 3 hours. In 1867 a sample was taken from a field 1,000 paces distant from the former, one portion of it was treat-— ed with boiling dilute acid (1 of concentrated acid to 20 — of water) for 3 hours. Another portion was digested for — three days with the same dilute acid, but without applica- — tion of heat. In each case the same substances were ex- © tracted, but the quantities taken up were less, as the acid ~ was weaker, or acted at a lower temperature. The follow- — ing statement shows the composition of each extract, cal- — culated on 100 parts of the soil. | q EXTRACT OF SOIL OF SALZMUNDE. q ' Hot strong acid. Hot dilute acid. Cola dilute acid. — Potash, 635 116 029 Soda, 127 067 .020 Lime, 1.677 1.046 1.098 Magnesia, 687 539 23% Oxide of iron and alumina, 7.931 3.180 -650 Oxide of manganese, .030 086 O71 Sulphuric acid, 059 039 .020 Phosphoric acid, -059 091 057 Silica, 1.785 234 1% Total, 12.990 5.398 2.357 The most interesting fact brought out by the above fig- — ures, is that strong and weak acids do not act on all the — ingredients with the same relative power. Comparing the — quantities found in the extract by cold dilute acid with — those which the hot dilute acid took up, we find that the latter dissolved 5 times as much of oxide of iron and alumina, 4 times as much. potash, 3. times as much soda, REVIEW AND CONCLUSION. 371 twice the amount of magnesia, sulphuric acid, and phos- phoric acid, and the same quantity of lime. These facts show how very far chemical analysis in its present state is from being able to say definitely what any given soil can supply to crops, although we owe nearly all our pre- cise knowledge of vegetable nutrition directly or indi- rectly to this art. The solvent effect of water on the soil, and the direct action of roots, have been already discussed (pp. 309 to 328). It is unquestionably the fact that acids, like pure water in Ulbricht’s experiments (p. 324), dissolve the more the longer they are in contact with a soil, and it is evident that the question: How much a particular soil is able to give to crops? is one for which we not only have no chemical answer at the present, but one that for many years, and, perhaps, always can be answered only by the method of experience—by appealing to the crop and not to the soil. Chemical analysis is competent to inform us very accurately as to the ultimate composition of the soil, but as regards its proximate composition or its chemical consti- tution, there remains a vast and difficult Unknown, which will yield only to very long and laborious investigation. Maintenance of a Supply ‘of Plant-food.—By the recip- ocal action of the atmosphere and the soil, the latter keeps up its store of available nutritive matters. The difficultly soluble silicates slowly yield alkalies, lime, and magnesia, in soluble forms; the sulphides are aia veried into sulphates, and, g Saale the minerals of the soil are disintegrated and fluxed under the influence of the oxy- gen, we water, the carbonic acid, and the nitric acid of the air, (pp. 122-135). - Again, the atmospheric nitrogen is assimilated by the soil in the shape of ammonia, ni- trates, and the amide-like matters of humus, (pp. 254-265). The rate of disintegration as well as that of nitrifica- tion depends in part upon the chemical and physical char- ‘acters of the soil, and partly upon temperature and mete- 372 HOW CROPS FEED, orological conditions, In the tropics, both these processes go on more vigorously than in cold climates. Every soil has a certain inherent capacity of production in general, which is chiefly governed by its power of sup- plying plant-food, and is designated its “ natural strength.” The rocky hill ranges of the Housatonic yield onee in 80 years a crop of wood, the value of which, for a given locality and area, is nearly uniform from century to cen- tury. Under cultivation, the same uniformity of crop is seen when the conditions remain unchanged. Messrs. Lawes and Gilbert, in their valuable experiments, have obtained from “a soil of not more than average wheat- producing quality,’ without the application of any ma- nure, 20 successive crops of wheat, the first of which was 15 bushels per acre, the last 17} bushels, and the average of all 164 bushels. (Jour. Roy. Ag. Soc. of Hng., XXV, 490.) The same investigators also raised barley on the same field for 16 years, each year applying the same quan- tity and kinds of manure, and obtaining in the first 8 years (1852-59) an average of 44{ bushels of grain and 28 cwt. of straw; for the second 8 years an average of 512 bushels of grain and 29 cwt. of straw; and for the 16 years an average of 48! bushels.of grain and 284 ewt. of straw. (Jour. of Bath and West of Eng. Ag.Soc., XV1,214.) | The wheat experiments show the natural capacity of the Rothamstead soil for producing that cereal, and de- monstrate that those matters which are annually removed by a crop of 164 bushels, are here restored to availability by weathering and nitrification, The crop is thus a measure of one or both of these processes,* It is probable * In the experiments of Lawes and Gilbert it was found that ee ogee sul- phates, and carbonates of lime, potash, magnesia, and soda, raised the produce of wheat but 2 to 8 bushels per acre above the yield of the unmanured soil, while sulphate and muriate of ammonia increased the crop 6 to 10 bushels, This re- sult, obtained on three soils, viz., at Rothamstead in Herts, Holkham in Nor- folk, and Rodmersham in Kent, the experiments extending over periods of 8, 3, and 4 years, respectively, shows that these soils were, for the wheat crop, rela- tively deficient in assimilable nitrogen, The crop on the unmanured soil was therefore a measure of nitrification rather than of mineral disintegration. REVIEW AND CONCLUSION, 373 that this native power of producing wheat will last unim- paired for years, or, perhaps, centuries, provided the depth of the soil is sufficient. In time, however, the silicates and other compounds whose disintegration supplies alka- lies, phosphates, etc., must become relatively less in quan- tity compared with the quite inert quartz and alumina- silicates which cannot in any way feed plants. Then the crop will fall off, and ultimately, if sufficient time be al- lowed, the soil will be reduced to sterility. Other things being equal, this natural and durable pro- ductive power is of course greatest in those soils which contain and annually supply the largest proportions of plant-food from their entire mass, those which to the great- est extent originated from good soil-making materials. Soils formed from nearly pure quartz, from mere chalk, or from serpentine (silicate of magnesia), are among those least capable of maintaining a supply of food to crops. These poor soils are often indeed fairly productive for a few years when first cleared from the forests or marshes; but this temporary fertility is due to a natural manuring, the accumulation of vegetable remains on the surface, which contains but enough nutriment for a few crops and wastes rapidly under tillage. Exhaustion of the Soil in the language of Practice has a relative meaning, and signifies a reduction of producing power below the point of remuneration. A soil is said to be exhausted when the cost of cropping it is more than the crops are worth. In this sense the idea is very indef- inite since a soil may refuse to grow one crop and yet may give good returns of another, and because a crop that re- munerates in the vicinity of active demand for it, may be worthless at a little distance, on account of difficulties of transportation. ‘The speedy and absolute exhaustion of a soil once fertile, that has been so much discussed by spec- ulative writers, is found in their writings only, and does not exist in agriculture. A soil may be cropped below the 374 -. HOW CROPS FEED. point of remuneration, but the sterility thus induced is of a kind that easily yields to rest or other meliorating agen- cies, and is far from resembling in its permanence that which depends upon original poverty of constitution. Significance of the Absorptive Quality.— Disintegration and nitrification would lead to a waste of the resources of fertility, weré it not for the conserving effect of those physical absorptions and chemical combinations and re- placements which have been described. The two least abundant ash-ingredients, viz., potash and phosphoric acid, if liberated by the weathering of the soil in the form of phosphate of potash, would suffer speedy removal did not the soil itself fix them both in combinations, which are at once so soluble that, while they best serve as plant-food, they cannot ordinarily accumulate in quantities destruct- ive to vegetation, and so insoluble that the rain-fall cannot wash them off into the ocean. The salts that are abundant in springs, rivers, and seas, are naturally enough those for which the soil has the least retention, viz., nitrates, carbonates, sulphates, and hydro- chlorates of lime and soda. The constituents of these salts are either required by vegetation in but small quantities as is the case with chlo- rine and soda, or they are generally speaking, abundant or abundantly formed in the soil, so that their removal does not immediately threaten the loss of productiveness. In fact, these more abundant matters aid in putting into circulation the scarcer and less soluble ingredients of crops, in accordance with the general law established by the researches of Way, Eichhorn, and others, to the effect that any base brought into the soil in form of a freely sol- uble salt, enters somewhat into nearly insoluble combina- tion and liberates a corresponding quantity of other bases. “The great beneficent law regulating these absorptions appears to admit of the following expression: those bodies which are most rare and precious to the growing plant are a : REVIEW AND CONCLUSION. BY hs) by the soil converted into, and retained in, a condition not of absolute, but of relative insolubility, and are kept avail- able to the plant by the continual circulation in the soil of the more abundant saline matters. “The soil (speaking in the widest sense) is then not only the ultimate exhaustless source of mineral (fixed) food, to vegetation, but it is the storehouse and conservatory of this food, protecting its own resources from waste and from too rapid use, and converting the highly soluble matters of animal exuvie as well as of artificial refuse (manures) into permanent supplies.”* By absorption as well as by nitrification the soil acts therefore to prepare the food of the plant, and to present it in due kind and quantity. * The author quotes here the concluding paragraphs of an article by him ‘‘On Some points of Agricultural Science,” from the American Journal of Science and - Arts, May, 1859, (p. 85), which have historic interest in being, so far as he is aware, the earliest, broad and accurate generalization on record, of the facts of soil-absorption. NOTICE TO TEACHERS. At the Author’s request, Mr. Louis Stadtmuller, of New Haven, Conn., will undertake to furnish collections of the minerals and rocks which chiefly compose soils (see pp. 108-122), suitable for study and illustration, as also the apparatus and materials needful for the chemical experiments described in ‘‘ How Crops Grow.” HOW CROPS GROW. A TREATISE On the Chemical Composition, Structure, and Life of the Plant, FOR ALL STUDENTS OF AGRICULTURE. WITH NUMEROUS ILLUSTRATIONS AND TABLES OF ANALYSES, BY SAMUEL W. JOHINSON, M.A., PROFESSOR OF ANALYTICAL AND AGRICULTURAL CHEMISTRY IN YALE COLLEGE 5 CHEMIST TO THE CONNECTICUT STATE AGRICULTURAL SOCIETY 5 MEMBER OF THE NATIONAL ACADEMY OF SCIENCES. This is a volume of nearly 400 pages, in which Agricultural Plants, or “ Crops,” are considered from three distinct, yet closely related, stand-points, as indicated by the descriptive title. THE CHEMICAL COMPOSITION OF THE PLANT. 1st.—The Volatile Part. 2d.—The Ash—lIts Ingredients ; their Distribution, Variation, and Quantities. The Composition of the Ash of various Farm Crops, with full Tables ; and the Functions of the Ash. 3d.—Composition of the Plant in various Stages of Growth, and the Relations subsisting among the Ingredients. THE STRUCTURE OF THE PLANT AND THE OFFICES OF ITS ORGANS. The Primary Elements of Organic Structure. The Vegetative Organs—Root, Stem, and Leaf, and their Funce-’ tions ; and The Reproductive Organs, namely, Flowers and Fruit, and tha Vitality of Seeds with their Influence on the Plants they produce. THE LIFE OF THE PLANT. Germination, and the conditions most favorable and unfavor- able to it. The Food of the Plant when independent of the Seed. Sap and its Motions, etc., etc. THE APPENDIX, which consists of twelve Tables exhibiting the Composition of a great number of Plants viewed from many different stand-points, will be found of inestimable value to practi cal agriculturists, students, and theorists. SENT POST-PAID. PRICE, $2. ORANGE JUDD & CO., 245 Broadway, New-York. 3477 4 on ae 9 eg Sms, ae. =a 7 a“ © Alig Goss in LIBRAR nn 3 U00e2