Apbil 17, 1908] 



SCIENCE 



635 



lines of transpiration and green weights in 

 plants in relation to the dry matter produced, 

 the observations covering the full life of the 

 crop, coming to complete and normal fruitage. 

 In the case where wheat seedlings were 

 grown a second time in the same supposedly 

 toxic solutions a better growth would be ex- 

 pected if these substances had the effect of 

 simply rendering the nutrients of the kernels 

 less readily transformed into available food, 

 and it is quite possible that crushed wheat 

 kernels placed in these solutions, thus elimi- 

 nating the vital activities of seedlings, might 

 have affected them as favorably as did the 

 growth of the first crop and might have caused 

 a disappearance or a reduction in the amount 

 of the toxic substance. These experiments, 

 therefore, can not be considered fully demon- 

 strative. For the same reason, and because 

 transpiration is not a measure of growth, the 

 experiments with nitrates and with lime are 

 also inconclusive. 



But granting that the data of Bulletin 47 do 

 demonstrate that the substances experimented 

 with are truly toxic to wheat seedlings under 

 the highly cramped and abnormal conditions 

 of the experiment, it will be conceded quite 

 rash to affirm that these substances in like 

 quantities would be found similarly toxic in 

 the soil under field conditions until it were 

 known, not only that such substances do exist 

 in the field soils, but also that they are more 

 abundant in those which are unproductive. 



The imwarranted publication of such posi- 

 tive conclusions as those quoted becomes still 

 more evident when an effort is made to give 

 quantitative expression to the recorded data 

 of Bulletin 47 in terms of field conditions cor- 

 related with other contentions of the Bureau 

 of Soils. It is maintained by the bureau, but 

 without sufficient evidence, that the capillary 

 movement of soil moisture under crop condi- 

 tions is of negligible magnitude and that for 

 this reason the roots of crops, in order to 

 secure moisture and plant food and also in 

 order to place the active absorbing root tips 

 into fresh soil not poisoned by their own 

 excreta, are compelled to constantly advance 

 into previously unoccupied soil, and they are 

 knovm to spread throughout a depth exceeding 



three to four feet in the case of most crops. 

 The toxic substances of unproductive soils 

 must, therefore, be deeply distributed through- 

 out the root zone and to a depth of at least 

 four feet. But the strongest solution used 

 in the experiments of Bulletin 47, of 1,000 

 parts per million, means not less than 2,800 

 pounds per acre of field where the water con- 

 tent of the soil is 20 per cent, and it would 

 mean 700 pounds per acre for the surface foot 

 alone. In the case of 100 parts per million 

 the amounts would be 70 pounds and 280 

 pounds per acre for depths of one and four 

 feet, respectively. In the light of failures up 

 to the present time to isolate these toxic sub- 

 stances from soils it will hardly be seriously 

 contended that any such large amounts of 

 toxic substances do exist in unproductive 

 soils. But the smaller amounts experimented 

 with, as recorded in Bulletin 47, either had 

 little or no effect or they produced positive 

 increases in growth. If, therefore, the data 

 of the bureau along this line of toxic sub- 

 stances are to be given serious consideration at 

 all, Bulletin 47 miist be regarded as suggesting 

 that on account of the probably small amounts 

 of these toxic substances present in soils, and 

 on account of their observed small, or else 

 stimulative, effect when present in such quan- 

 tities, toxic substances are either negligible 

 factors in soil fertility or else they are bene- 

 ficial to crops. F. H. EJtNG 

 Madison, Wis. 



SPECIAL ARTICLES 



a new apparatus for measuring electrolytic 

 resistance' 

 The measurement of electrolytic resistance 

 differs from that of a metallic conductor in 

 several respects. The most evident difference 

 is that the electrolyte has no definite shape or 

 size. Cells of various forms have been devised 

 to hold the solution while it is being measured 

 and I would hardly venture to add another 

 to the list were it not for the fact that the 



'Paper read before Section B of the American 

 Association for the Advancement of Science and 

 the American Physical Society in joint session, 

 Chicago, December 31, 1907. 



