October i, 190S] 



NA TURE 



541 



done at Leeds if they aulliorise the secretary to state " they 

 have satisfied themselves that this evidence is erroneous." 

 Those who in common with myself have lootted critically 

 and, I may say, quite impartially into the evidence have 

 come to the conclusion that the analytical methods are 

 quite dependable. Others will no doubt corroborate this 

 statement. After the publication of the report the Planters' 

 Association held a meeting, at which they passed a resolu- 

 tion expressing confidence in, and practically endorsing 

 the opinion of, their own advisers, in face of the new 

 evidence offered from the Leeds laboratory. I gathered 

 this information from a report of the meeting in one of 

 the Indian papers, which was forwarded to me at the 

 time. This attitude, which may fairly be described as one 

 of hostility, would have been stiffened by the above letter 

 were it not therein admitted that the " biological side " 

 of the problem is still in its infancy, and that further 

 development in this direction is anticipated. Also it is 

 conceded that " an entirely independent opinion " in the 

 matter (? of the manufacturing processes) is to be 

 obtained. Thus all the contentions of those who felt the 

 ignominy of this great Indian industry " taking its 

 whipping in a crouching attitude " are likely to be met, 

 and our bes^wishes are, it is needless to say, with the 

 planters. If (hey are, by the inexorable laws of nature, 

 beaten in the long run, it will at any rate redound to their 

 credit that they did not succumb without a good fight. 



There is one point in the foregoing letter which appears 

 of considerable importance, and to which I should like 

 to take the present opportunity of directing attention. 

 The evidence of the advisers to the association is accepted 

 because it appears that they are on the spot and dealing 

 with the fresh plant, while the Leeds chemists have been 

 investigating " preserved material." Now if the Leeds 

 results by the isatin method are correct — and I repeat 

 that I see no reason to doubt them — it follows that '" pre- 

 servation " leads to an increased development of indican. 

 May not this hint be worth following up practically? In 

 thanking the secretary of the association for his com- 

 munication, I should like, in conclusion, to repeat what 

 1 said during the discussion before the Society of Chemical 

 Industry last autumn. The results given by the newer 

 methods of analysis mav be unrealisable in practice ; it 

 does not follow that because a certain percentage of 

 indican is present in an Indigofera leaf the corre- 

 sponding Quantity of indigotin, or anything approaching 

 that quantity, can be got out of it in the factory. All 

 that is contended is that at the present juncture the indica- 

 tions furnished bv a scientific quantitative method render 

 it imperative that everv resource should be strained to 

 save the native industrv. Further developments will be 

 anxiously waited for in this country. 



R. Meldola. 



I ENTIRELY agree with the opinion expressed by Prof. 

 Meldola in his article, entitled " A Contribution to the 

 Indigo Question," which recently appeared in N.^ture 

 (p. 2q6), that the case had " at one period assumed a 

 polemical aspect most detrimental to the real cause at 

 issue," and I write this with no desire to discuss the 

 responsibility for this regrettable state of affairs, or to 

 revive it. My object is to record some results recently 

 obtained by Mr. Briggs and myself, which we had not 

 intended publishing, but which may prove of interest in 

 the light of Prof. Meldola's article. 



.Anhydrous indican was prepared according to the methcxl 

 of Perkin and Bloxam (Journ. Chem. Soc., vol. xci., p. 

 1715) ; its melting point was, as statetl by these authors, 

 176—178°. A gram of this substance was dissolved in 500 

 CO. of water. Two 100 c.c. samples were withdrawn from 

 this solution, and analysed by the isatin method of Orchard- 

 son, Wood, and Bloxam (journ. Soc. Chem. Ind., vol. 

 xxvi., pp. 8 and 1178). and two by the persulphate 

 method of Bergtheil and Briggs (Journ. Soc. Chem. Ind., 

 vol. XXV., p. 734, and vol. xxvi., p. 1173). This was 

 repeated three times with two distinct preparations of 

 indican. The following results, expressed as the amount 

 of indigotin (in grams) to be derived from 100 c.c. of the 

 solutions, were obtained. The figures are means of the 

 duplicate experiments, which agreed very closely. 



NO. 2031, VOL. 78] 



Persulphate theory 



method 



o -0^401 



Isatin 

 method 

 1. O0S4I 



ii. ooiSss 

 iii. 00S52 o'o845j 



The indirubin obtained by the isatin method was analysed 

 by titration with titanium chloride (Knecht) in each case, and 

 found to be g8 per cent, pure (average of si.x samples) ; the 

 titanium chloride solution was standardised on pure iron, and 

 also on pure indigotin obtained by sublimation under 

 reduced pressure (Bloxam). 



The indican employed was evidently not pure, the analyses 

 indicating a purity of 94-6 per cent, in the first case, and 

 95-6 per cent, in the second and third, but this degree of 

 purity is sufficiently high for the purpose of comparing the 

 methods. The comparisons indicate that almost identical 

 results are obtained, the mean difference being 07 per 

 cent. 



Another point which these figures seem to establish is 

 the accuracy of our method of determining indigotin (at 

 any rate, so far as the factor for the relationship between 

 indigotin and permanganate is concerned), for it is ex- 

 tremelv improbable that, were an error involved in this 

 method, it would be so exactly counterbalanced by errors 

 in the other direction in the precipitation of indigotin by 

 persulphate as to bring the results into such close ap- 

 proximation with those obtained by the isatin method. 



If these two points are conceded, then the main grounds 

 on which the contention is based, that " the older methods 

 have overestimated the indigotin content of the dried 

 cake, and have underestimated the amount of indican in 

 the leaf," disappear. C. Bergtheil. 



Sirsiah, September 2. 



An Alleged Excretion of Toxic Substances by Plant 

 Roots. 



.Since the communication entitled " An Alleged Excre- 

 tion of Toxic Substances by Plant Roots " appeared in 

 N.^TURE (August 27, p. 402), it seems desirable to state 

 the exact position taken by the Bureau of Soils on the 

 question of deleterious substances in soils and root excre- 

 tions. • 



.Abundant evidence has already been presented to the 

 effect that substances deleterious to plant growth do exist 

 in many soils, and are mainly responsible for the in- 

 fertilitv therein observed,' and toxic substances, to wit, 

 picoline carboxylic acid and dihydroxystearic acid, have 

 actuallv been isolated and identified. In carefuUv con- 

 trolled experiments these toxic conditions have been shown 

 to arise as the result of the continuous growth of the 

 same sort of plants upon the soil. In addition, it has been 

 shown that plants like wheat excrete substances which 

 set up toxic conditions in the medium. Toxic conditions 

 may also arise from the presence of the decomposition 

 products of vegetable matter in the soil. Indeed, it has 

 been shown that verv many substances naturally occurring 

 in plants are toxic in quite small amounts. When plants 

 containing these substances are incorporated with the 

 soil, they may play an important nl/e as soil constituents. 



Regarding the criteria of growth, it may be said that 

 not transpiration alone, as implied in the article referred 

 to, but several standards of growth were employed in the 

 investigations of this bureau, viz. weight of green tops, 

 dry weight, transpiration, turgidity and colour of roots, 

 chemotropic response of the roots. -All these criteria 

 are employed in determining the physiological effect of 

 substances on plants, but no one is regarded as absolute. 



The statements made in Bulletin No. 48 of this bureau 

 were based, as was said in the note referred to, upon 

 many thousands of pot experiments, and the conclusions 

 seem justified by the results of that work. It is obviously 

 possible to choose figures from any table which are appar- 

 ently discordant. A comparison of the paraffin pot method 

 of testing soils with the results of continuous plot experi- 

 ments in this country has shown good agreement." 



How.^RD S. Reed. 



.Agricultural Experiment Station, Blacksburg, Va. 



1 Bulletins Nos. 28. ^d, 40 and 41 Bureau of SoiU : Rept- Hawaii Agr. 

 Exp. Sta., 1906. p. 37 : Tourn. Biol. Chem., iii., Proc. 38 (1907) ; Journ. Amer» 

 Chem. Soc, -\xx , 120=; (rcjoS); Science, xxvii., 190, 295, 328, 329 (igo8). 



~ Bull. 109, Rhode Island Agr. Exp. Sta. 



