October x, 1SS5.] THE TROPICAL AGRICULTUKIS.T. 



255 



E. corymbosa, E. diversicolor, and E. obliqua come 

 next in value; E. rediinca, E. resiaifera, and E. 

 cornuta arc also mentioned as yielding excellent timber. 

 A remarkable use is made by the natives of the 

 roots of E. micrantbera. These are lifted up from 

 the depth of about a foot, and at a distance of 

 about 15 feet from the tree; they are theu cut 

 up into pieces, about as thick as a man's wrist and 

 about 18 inches long, and are allowed to drain into 

 a vessel, or blown into by the mouth at one end. In 

 this way a quart of water may be obtained from 

 good samples in about half-an-hour. Eoots nearer the 

 stem are less porous, and do not yield water so 

 easily. The water is stated to be beautifully clear, 

 cool, and without any unpleasant taste. The roots 

 of E. oleosa and E. populifolia are used for the 

 tame purpose, but yield water less readily. — Gardeners' 

 Chronicle. 



DO PLANTS ABSORB ATMOSPHERIC 

 NITROGEN ? 



Probably no doctrine in the whole realm of agri- 

 cultural chemistry makes a greater impression on the 

 mind of the student who hears it for the fii'st 

 time than that which teaches that, although four- 

 fifths of our atmosphere consists of free nitrogen 

 gas, plants are nevertheless unable to assimilate this 

 valuable ingredient directly from so inexhaustible a 

 reservoir. To every farmer the doctrine is brought 

 home forcibly and practically enough in the sums of 

 money he pays away iu the purchase of nitrate of 

 soda and other nitrogenous fertilizers. The experi- 

 ments, well termed classical, of Boussingault on 

 the one hand, and of Lawes, Gilbert, and I'ugb on 

 the other, were regarded for a long time as setting 

 at rest any doubt which might be entertained on the 

 subject. And yet in later years the Kothamsted 

 investigators themselves have felt some difficulty, 

 and have suggested perhaps somewhat extreme hypo- 

 theses, to account for the behaviour of leguminous 

 crops, which, after providing themselves with the 

 large amount of nitrogen they are known to require, 

 yet leave more nitrogen in the soil than the latter 

 contained at the beginning of growth. Facts such 

 as these are sufficient to justify the increasing feel- 

 ing of scepticism as to whether the nitrogen ques- 

 tion — for such we may briefly term the discussion 

 as to the sources of the nitrogen of vegetation — has 

 been fully sifted, or whether more remains to bo 

 discovered. In any case, it is a difficult point, which 

 can only be settled by the most laborious and 

 exact experiment, and the few remark.s we have 

 matle are simply prefatory to passing briefly under 

 notice some recent investigations by Mr. W. O. At- 

 water, of Middletomi, Conn., " On the acquisitiou 

 of atmospheric nitrogen by plants," the full report 

 of which appears in the American Chemical Journttl. 



Tlie investigator rightly observes that it is very 

 difficult to explain how certain plants, particularly 

 legumes, obtain their nitrogen, if not from the air, 

 8ud he sets himself to attack the problem as to 

 whether plants, grown under normal conditions, ac- 

 quire any considerable amount of nitrogen from the 

 surrounding atmosphere. Two sorts of experiments 

 Were made, the plants employed being "Early 

 Philadelphia" dwarf peas. It is not neces-sary to 

 give the details of manipulation, but every care 

 appears to have been taken by the experimenter. 

 The first series of experiments showed in every case 

 an excess of nitrogen at the end of the experiment 

 over that contained in the mamirial solution and in 

 the seed, while the more detailed experiments of the 

 second series gave larger gains of atmospheric nitro- 

 gen. Rain and dew, which carry down nitrogen 

 in solution, were prevented from gaining access to 

 the plants. 



In those e.iperimenta in which the conditions of 

 growth were approximately normal, the excess of nitro- 

 gen in the plant over that supplied by the nutri- 

 tive solution with which the plants were watered, 

 •nd by the seed, averaged i)0 lb, per acre. In the 



case in which there was no considerable apparent 

 hindrance to normal growth the appropriated nitro- 

 gen rose to 122 lb. per acre— twice as much as the 

 total nitrogen in grain and straw of a wheat crop 

 of thirty bushebi, and more than the total nitro-eii 

 of three tons of clover hay. And, observes the author, 

 this remarkable gain caunot rejiresent more, and' 

 may be les.s, than the actual quantity of atmospheric 

 nitrogen which the plants acquired during the brief 

 period of seventy-two days of growth. 



In discu.ssing the results the lirst question asked is, 

 was the atmospheric nitrogen absorbed directly by the 

 foliage of the plants, or was it first ab-sorbed by the 

 nutritive solutions and thus communicated to the plants 

 through their roots ? Experimental and other evidence 

 is adduced to show that the plants in which the conditions 

 of assimilation were most nearly normal, absorbed an 

 amount of nitrogen which was probably more than 47 per 

 cent of the total nitrogen of the plant (equivalent to 

 ILS lb. per acre), which could have come from no other 

 source than the atmosphere, and through no other 

 channel than the leaves. 



It is next inquired, Was the atmospheric nitrogen 

 acquired by the plants in the form of combined 

 nitrogen ? Of course, this nitrogen must have been 

 either free or combined, but the author quotes Sir 

 Johu Lawes and Dr. Gilbert to the effect that the 

 broad-leaved root crops, turnips and the like to 

 which the formation has with most confidence been 

 attributed, do not take up any material proportion 

 of their nitrogen by their leaves from combined nitro- 

 gen in the atmosphere. But Mr. Atwater, although 

 he admits that plants do obtain some combined iiitro- 

 geu iu the atmosphere, maintains that in his own 

 experiments the supposition that the plants could 

 have obtained more than a fraction of their atmo- 

 spheric nitrogen in this form is out of the question. 



The only possible remaining question is, Did the 

 plauts acquire free nitrogen Irom the atmosphere? 

 To answer this question in the affirmative is to 

 enter the lists against all the best authorities on the 

 subject. Mr. Atwater points out that the experi- 

 ments that are most decisive against the assimilation 

 of free nitrogen, namely, those of Boussingault and 

 of Lawes, Gilbert, aud Pugb, weiu conducted under 

 gla.-:s covers connected with the earth. Berthelot 

 has shown that tree nitrogen may bo assimilated 

 by vegetable substances — de.v trine cellulose, &c.. un- 

 der the influence of electricity of tenisou similar to 

 that which a brick obtains near the surface of the 

 earth, iu the strata of air iu which our cultivated 

 plants grow. It may be inferred that the compounds 

 in living plants nuiy asimilate nitrogen iu the same 

 way. But this electrical tenisou might probably be 

 abseut iu the experiments with plants uuder glass. 

 So Jlr. Atwater thinks that the hypothesis of the 

 assimilation of free nitrogen ly plants through the 

 agency of electricity, aud the absence of that agency 

 in the experiments of Boussingault, aud of Lawes, 

 Gilbert, aud Pugh, would, with the effect of scanty 

 food supply, e.xplaiu the discrepancy between their 

 experiments and his own, in which the conditions 

 of growth were normal, and which would clear up 

 the greatest difficulty in this niuch-ve.xed question 

 of the sources of nitrogen of plants. 



AVe can sympathize with the author's desire to 

 interpret his own results iu such a way as shall be 

 consistent with tliose obtained by the reuowued in- 

 vestigators of Kothamsted. Much— we may say every- 

 thing—depends on the scrupulous care with which 

 the experiments have lieeu conducted. I'resumiug 

 they are thoroughly trustworthy— ajul theju does not 

 appear any i;viilence to the contrary— the nitrogen 

 question is presented to us in a new and interesting 

 light, and it is possible that we may now be on the 

 threshold of a fresh stage of the eontrover.sy, the 

 ultimate settlement of whiih may not unlikely be 

 fraught with a great, a significant, and a salutary 

 modification of some of the cardinal practices of 

 modern .agriculture. — Mark Lane I'Jxjyrcss. 



[The above article has been sent to us by the 

 writer, Mr. John Hughes, who made reference to 



