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numerous cankers similar to those on the larch. There is no reason to suppose that this locality is the only one where the disease occurs; indeed the reverse is practically sure to be the case, as it is well known that European larch was imported widely and quite generally twenty to fifty years ago. The fact that it can go onto so many different American species, which are important timber trees, makes this discovery of very serious importance to all parts of this country. Further scouting is being done to see if it is widely distributed.

PERLEY SPAULDING, PAUL V. SIGGERS

BUREAU OF PLANT INDUSTRY AND NORTHEASTERN FOREST EXPERIMENT STATION

THE DEFICIENCY OF ENGLISH UNITS OF
MEASURE AND WEIGHT FOR SCIEN-

TIFIC AND TECHNICAL USES
THERE are certain deficiencies in the English mea-
sures and weights which may be ascribed to historical
causes and which have been imperfectly supplied by
the use of troy and metric small denomination units.
But the troy and metric units are not commensur-
able with the common or English units. The cause
of this deficiency is that the English units were devel-
oped for the uses of trade, construction and manufac-
ture, to which purposes they are perfectly adapted.
The demand for technical, scientific and precision
units is a relatively modern demand.

The English measures have no unit lower than the pinch, whereas the metric system has seven such units,

vis., centimeters, millimeters, microns, angstroms, millimicrons, milliangstroms and micromicrons, of b which the inch contains 2.54 centimeters, 25.4 millimeters, 25,400 microns, 254,000 angstroms, 25,400,000 millimicrons, 254,000,000 milliangstroms and 25,400,000,000 micromicrons.

of the foot, the dram the cube of the twentieth of the foot and the moit the cube of the hundredth of the foot of water at the maximum density. The common eight-ounce cup is the cube of two tenths or of one fifth of the foot. This will supply the deficiency of common units lower than the inch and the ounce, made necessary by modern refinements in measuring dimensions, volumes and masses.

For definitive purposes it is proposed that the foot be taken as the length of 473,404 waves of red cadmium light, that the ounce be taken as the weight of 28,316 milligrams and that new material standards or master bars and weights be constructed from these definitive values.

The avoirdupois pound was anciently regarded as equal to 7,002 troy grains. In 1844, however, after the burning of the parliamentary standards, the pound for the sake of certainty was defined by parliament as the weight of 7,000 troy grains, which produces 437.5 grains to the ounce.

The proposal to define ounce as 28,316 milligrams recognizes 28,316 grams as the weight of the cubic foot of water under the definition of the foot as 473,404 red cadmium waves. This takes 34 milligrams off the ounce, which for practical purposes may be regarded as one-half grain of 32.4 milligrams, thus reducing the ounce roughly from 4371⁄2 to 437 grains.

It is quite as legitimate to give the ounce a definition in milligrams as it was to give the pound a definition in troy grains, as was done more than eighty years ago. This is the one way to coordinate the ounce with the cubic foot of water and to correlate common volumes and weights.

WASHINGTON, D. C.

SAMUEL RUSSELL

"WASHBOARD" OR "CORDUROY" EFFECT DUE TO THE TRAVEL OF AUTOMOBILES OVER DIRT ROADS

THE interesting account of the so-called "washboard" or "corduroy" effect due to the travel of automobiles over dirt roads calls to mind an experience which the writer had last summer in the northern part of Minnesota.1 Professor Dodd's explanation is very much to the point and on the whole I think plausible, but I am not sure that the explanation has gone far enough. In the single instance observed, my motor car was following a "grader" over a newly graveled stretch of road and, since I had myself advanced several theories concerning the cause of this

1 Dodd, L. E., "'Washboard' or 'Corduroy' Effect Due to the Travel of Automobiles over Dirt Roads," SCIENCE 66, 1927, 214–216.

frequent phenomenon, I was very much interested to see that my theories were wrong, especially at the beginning of the causal series. Many of the corrugations that I had noticed were somewhat slanting, and now I saw that the scraping blade of the grading machine was responsible for the original vibration which was left in the road.

I have no doubt that the wheels of cars which travel on newly graded roads very much deepen these ridges when they resonate in tune to the original vibration of the scraping blade of steel which has left its marks in the ridges on the road. It must not be forgotten, too, that rain falling on the road will then also tend to drain off along these ridges and deepen them by erosion. I am wondering, too, when the road is of a certain elastic consistency, with a slight amount of moisture in the top layer, whether it will not then act much in the same fashion as the

Boron was the next of these elements to receive attention. Warrington3 in 1923, showed it to be essential for broad beans (Vicia Faba) and probably for runner beans, crimson clover (Trifolium incarnatum) and Trifolium multiflorus, but reported inconclusive results for white clover (Trifolium repens) and peas and negative results for barley and rye. The writer in experiments with silicon and aluminum in which purified salts were used, confirmed the results with broad beans. The "mason" jars in which the solution culture experiments were being carried out were coated with "Valspar," a resistant varnish, to prevent contamination by solution of the glass, and sufficient boron for apparently normal growth of wheat, peas, millet and Penisitum vilosum was furnished by the varnish. Broad beans, however, made very little growth and showed the symptoms described

by impact, especially on down grades.

Naturally, this was only a single instance that came under my observation, but I made sure that there were no corrugations in front of the grader and that there were characteristically slanting and partially formed ones behind, and I am offering this bit of discussion in the hope that the matter may be verified or contradicted by observations of others. In general, this additional cause does not contradict the excellent explanation of Professor Dodd, but goes simply one step farther in certain cases.

THE UNIVERSITY OF IOWA

CHRISTIAN A. RUCKMICK

THE SEARCH FOR ELEMENTS ESSENTIAL IN ONLY SMALL AMOUNTS

FOR PLANT GROWTH

FOR many years the essential nature of certain elements for normal plant growth remained undiscovered because they are needed in such small amounts that they were supplied as undetected impurities in the media in which the plants were grown. Between the years 1910 and 1919 Mazé,1 by careful technique, I showed boron, zinc and manganese to be essential to the growth of maize. Possibly because most of his papers were published in a journal devoted chiefly to bacteriological literature, they were overlooked by most plant physiologists. It was not until 1922 that the work of McHargue emphasized the essential

nature of manganese.

1 Mazé, P. Ann. Inst. Pasteur. 1914, 28, 21-68; 1919, 33, 139-173. Comp. Rend. Acad. Sci. 1915, 160, 211-214. 2 McHargue, J. S. Jour. Amer. Chem. Soc. 1922, 44, 1592-1598.

normal growth when .5 mg. per liter of boron as boric acid was added to the solution. Later on when using uncoated jars in an experiment to determine whether or not chlorine is essential to plant growth, buckwheat failed to develop beyond the cotyledon stage when purified salts were used but developed normally when the ordinary "C.P." analyzed salts were employed. Because of the experience with broad beans, absence of boron was suspected of being the limiting factor. Investigation showed this to be the case. This and the effect of boron on the growth of sunflowers led the writer to study the effect of the absence of boron on a number of plants. Part of this work with that continued at the University of California and later at the University of Minnesota, showed boron to be essential to corn, peas, sunflowers, vetch, barley, buckwheat, dahlias, lettuce, potatoes, millet, castor beans, sugar beets, kafir, sorghum, flax, mustard and pumpkins. Plants differed in the time, and to some extent in the way, in which the effect first appeared but none of the plants reached the flowering stage. Dicotyledonous plants in general responded more quickly than did monocotyledonous plants. In the case of sunflowers, cotton and buckwheat, the tops did not develop beyond the cotyledon stage and the roots grew very little. Other dicotyledonous plants showed the lack of boron by suppressed roots with enlarged apices within a few days but, depending on the type of plant, produced from

8 Warrington, Katherine. Ann. Bot. 1923, 37, 629-672. 4 Sommer, A. L. Agri. Sci. Series, Univ. California 1926.

5 Sommer, A. L. and Lipman, C. B. Plant Phys. 1926, 1, 231-249.

two to eight leaves. Soy beans were an exception; neither the tops nor the roots showed the effects of the lack of boron for two weeks. In this case also In the roots were the first to show the effect. Monocotyledonous plants grew for a greater length of time and produced much better root systems than did the dicotyledonous plants. Many of these plants showed abnormal tillering as well as withering of the growing points of the tops. Corn showed the effects of the lack of boron in a week, but continued to produce small tillers for some time. Barley, under winter greenhouse conditions, apparently grew normally for a month, but after that the difference between the plants without boron and the controls developed rapidly. Bermuda grass (the only plant investigated which did not show marked injury in the absence of boron) is still under investigation, and so far has given very doubtful results. It is a very resistant grass and after an initial addition of iron to the culture solution, grew well and with no signs of chlorosis, without further additions of iron, during a period of two months while the writer was pabsent.

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It is interesting to note that in a recent paper by Brenchley and Warrington, buckwheat and potatoes are among the plants reported to have given inconclusive results and that peas completed normal development without boron. These results, as well as some reported in Warrington's earlier paper, are in marked at contrast to those obtained by the writer. Whether this is due to a difference in technique or to the amount of boron stored in the seed is a point still to be investigated, but the fact that these authors obtained better growth without the addition of boron when they changed the solutions frequently suggests that the salts which they used may not have been entirely free from boron. In the case of the potato, the writer did not use seeds but allowed the tubers to sprout, removed the sprouts and transferred them to culture solutions.

Zinc, of the three elements mentioned above, is the one in which the conditions of experimentation must be most carefully controlled. The ordinary glass "mason" jar, in which many solution culture experiments are carried out, apparently furnishes all the zinc the plant needs. It was not until an attempt was made to use pyrex beakers with purified salts that the need of zinc was suspected. Solutions of the same salts which had produced good plants in ordinary glass failed when pyrex was employed. Wheat grew well for about two weeks and then stopped growing, turned yellow and finally died. The roots

* Brenchley, W. E. and Warrington, Katherine. Ann. Bot. 1927, 41, 167–187.

on the other hand were in good condition when the tops were dry and apparently dead. The analyses published by McHargue in which zinc was found in seeds led the writer to try zinc which was found to be the limiting factor. It was not until the experiments with barley and sunflowers were completed that the paper by Mazé, in which he showed zinc to be essential for maize, was discovered in the literature. As in the case of the lack of boron, recovery from the lack of zinc can be accomplished by the addition of .5 mg. of the missing element per liter to the culture solution. Smaller quantities may be sufficient, but were not tried.

Zinc was shown to be necessary for barley, sunflowers, wheat, buckwheat, broad beans and red kidney beans. Buckwheat, sunflowers, barley and wheat showed the effects of the absence of zinc in the early stages of growth; wheat and barley died in the early stages, while some of the sunflowers and buckwheat plants, although much smaller than the controls, produced a few small flowers. The broad beans and red kidney beans without zinc appeared to grow as well as the controls until they reached the flowering stage. At this stage, the plants declined rapidly; most of the leaves fell off and only a few flowers on the broad beans developed. No seed was produced by the plants without zinc, while those with zinc developed normally.

When pyrex glass was used, silicon and aluminum, and later traces of other elements, including copper, were added to the solution. Barley failed to make good growth in pyrex containers unless silicon was added and there was some indication that copper is also necessary.

A study of these problems has shown that it is only by exercising the greatest precautions that we may solve the problem of essential elements. The salts must be repeatedly crystallized from pure distilled water (essentially conductivity water) and in some cases be derived from elements and acids or from other salts, for the "C.P." salts of trade usually contain, as impurities, sufficient amounts of certain elements to produce normal plant growth. Contamination by dust and in some cases other impurities in the air (for example, chlorine, in chlorine studies) must be carefully avoided. The type of container is also an essential factor. The ordinary glass jar must be avoided in many cases because of its solubility. Pyrex is suitable for most work, and, although a boro-silicate, does not yield sufficient silicon and boron for the normal growth of at least some plants. The effect of the lack of boron, how

7 McHargue, J. S. Jour. Amer. Soc. Agron. 1925, 17, 368-372.

should be freshly ignited.2) The solution remains clear for some time and on standing, more rapidly after agitation, crystals of ammonium magnesium phosphate make their appearance.

Titrate with 5/N HCl to a reaction of approximately pH 7.0-7.6 and add an equal volume of distilled water.

Procedure and results.-This decalcifying fluid is apparently efficient in softening bone after it has undergone the action of any of the common fixing agents, but it is perhaps better to fix and harden the specimen in formalin. The latter must be well washed out from the tissue, first in running water for 12-24 hours according to the size of the specimen, and then in two or three changes of distilled water. It is then ready for decalcification. The citrate solution should be changed fairly frequently, since it will otherwise dissolve the calcium salts to saturation and the reaction will then retard. It has seemed best to replace the solution every other day. Decalcification proceeds relatively slowly as compared with solutions of the strong acids such as hydrochloric or nitric but it is much more rapid than Muller's fluid, picric or chromoacetoosmic acid, for example. The rib of a dog split through the center is freed of lime salts by this solution in about fifteen days. Swelling of the tissues is not induced by the fluid and there is no apparent shrinkage of such cells as those of the bone marrow. Stains are taken up without difficulty and sections stained with haematoxylin and Eosin colored in tints much more pleasing to the eye than those obtained when the application of the stain has been preceded by decalcification with strong acids. Magnesium citrate solutions are not so satisfactory as is Muller's fluid, however, if determination of the amount of uncalcified osteoid tissue present in the bone during the life is requisite. Unlike Muller's fluid, magnesium citrate allows decalcification to go on to completion and removes all possibility of distinguishing

2 This reagent has been used by Mathison, G. C., Biochem. Jour., 1909, IV, 237; Fiske, C. H., Jour. Biol. Chem., 1921, XLVI, 289, and by others.

SPECIAL ARTICLES

E.M.F. INDUCED IN A STRAIGHT WIRE BY A CURRENT IN A PARALLEL STRAIGHT CONDUCTOR

IN Figure 1, let A be a cross-section of a tubular conductor of practically infinite length, and let a current, i, in this conductor flow "in," as shown by the crosses. Another long conductor, B, of small cross-section, is placed along the geometrical axis of A, and the ends of B are left open. It is required to compute the e.m.f. induced in B, per unit of its length, when the current in A varies with time at the rate di/dt.

Reasoning I. The magnetic lines of force outside the tube A are concentric circles, such as H. Within the wall of the tube they are also concentric circles. Inside the tube, the magnetic flux density is zero at any value of i. Consequently, no flux cuts B or collapses on it when the current i is varied, and no e.m.f. is induced in B.

Reasoning II. Consider two diametrically opposite filaments of current, such as f and f', and determine the e.m.f. which a varying current in these filaments would induce in B. The three conductors are shown separately in Fig. 2. Let h be a line of force due to f, and h' a line of force due to f'. Let the currents in f and f' decrease; the motion of the two fluxes is then as shown by the horizontal arrowheads, each flux "collapsing" towards its own conductor. With