POISONS AFFECTING PLANTS. These are few in number, and principally mineral. -Of gases, the common illuminating gas is the only one to be feared, acting fatally, when from leakage of the underground pipes, it is taken up by the roots. Plants quickly suffer if kept in rooms lighted with gas, and hence the reason why florists refuse to leave rare plants long on exhibition at public places lighted with gas. It has been generally credited that Paris Green acts injuriously to plants when used for destroying insects, and many think that it may be taken up to such a degree a,s to become poisonous to persons eating the fruit. This, however. is groundless, except when the poison may have been applied, and lodging on the fruit or vege table to be eaten, and taken into the stomach. Hence poisonous compounds should never he used on plants, the fruit of which is designed for eating after the season of inflorescence. This will not apply to underground tubers, like potatoes; upon cabbage, cauliflower and other plants which may retain the poison, it should not be used at all. Among the mineral poisons fatal to vegetable life, the compounds of boracic acid have been found to be a veritable plant poison. M. Peligot has discovered that the free acid, and its compounds, when present in the soil in moderate quantities may cause the death of plants in a short time. A remarkable excep tion to the rule for the influence of aluminium -salts is said to have been observed by Bergstrand, in a locality near Westerbotten, in Sweden, Rubus articus was found in a flourishing condi dition upon a sandy soil containing as high as three per cent. of alum. The dry plants yield 4.68 per cent, of ash, containing 12.60 per cent. sulphuric acid and five per cent. alumina; but these figures are very much reduced when the percentage of alum in the soil is sufficiently low to admit of the growth of grass and grain. In such case the sulphuric acid of the ash amounts to only five per cent. In relation to the influ ence of arsenical compounds, when present in the soil, the chemist of the Department of Agri culture, in a late report, gives the results of interesting and conclusive experiments of rnuch value, showing that there is but little to fear. The investigation was made to determine: 1 If applied to the soil, can arsenic or arsenious acid be absorbed and assimilated iu the economy of plant-growth? 2. lf absorbed and assimi lated, can it be taken up in sufficient quantity to become prejudicial or injurious to the health of consumers? 3. If not talKen up by the plant during growt'a, does it by its presence in the soil exert a poisonous influence upon the plant itself ? 4. If it exerts a poisonous influence upon the plant, to what extent may it exist in the soil before it becomes injurious? The experiments were conducted as follows: Fifteen common flower-pots, of as nearly uniform size as possible, were selected, and each one filled with a meas -ured quantity of good garden-soil. With the soil of each pot were then thoroughly intermixed quantities of Paris Green, ranging from 100 milligrams to one gram. Thus one pot contained 100 milligrams; that next to it contained 200 milligrams; the next 300; and this quantity was increased until it finally reached one gram. ln the other pots, the increase was made more rapid, and the other pots contained two, three, four, and five grams respectively. After the soil had thus been carefully prepared, a given num ber of peas, all or which were carefully selected, so as to secure as nearly as possible those of the same size and appearance, were planted in each pot. At this time, the question arose, What would be the effect of arsenic in combination, as arseuite of potassa and arseniate of potassa? For the purpose of determining this, two other series of pots were prepared in the same rnanner as before, placed alongside the former. In these experiments, for the sake of comparison, one pot of soil was prepared without addition of any poisonous compound. It is evident from results that the arsenical compounds in the soil did pro duce an injurious effect, and in some instances, in fact in the majority of them, it was decidedly marked. In case of the Paris Green,. it is not noticed until the quantity present in the soil reaches 500 milligrams, and that in the other pots the size of the plants decreases regularly as the quantity of arsenical compound present increases. In case of the arsenite of potassa, the effect seems to be nmre immediate. This may be due either to the greater solubility- of the compound or to a possibly larger quantity of arsenious acid. The potash compound seemed nearly pure, being crys'allized, and the purity of the copper com pound was not estimated. Yet in this case the effect does not seem decidedly marked until the quantity present reached 300 milligrams. To the influence of arseniate of potassa the plants seemed to be more sensitive stilf; for those in the pot containing but 100 milligrams seem to be affected. Yet even when 200 milligrams are present, the plants seem to thrive tolerably well. What. then, are the quantities of these com pounds which may be applied to the soil for the various purposes in practical agriculture before effecting any injurious results? The amount of soil in each or the pots employed in these experi ments was 91.5 cubic inches. In case of the Paris Green, the limit is 500 milligrams for this quantity of soil, which is equivalent to 145.6 grams per cubic foot, or 906.4 pounds per acre, calculating for a depth of oue foot. The limit for arsenite of potassa, being 300 milligrams per 91.5 cubic inches, is about 540 pounds per acre. Though the plants seetn to be affected by even a small quantity of arseniate of potash in the soil, the chemist was nevertheless inclined to the opinion that this compound may be applied at the rate of 150 pounds per acre without any great injury to the crop. For practical pur poses, however, it is never necessary to apply in any case so large an amount. These results are confirmed by the water culture experiments of Prof Freytag in his investigations upon the intiuence of the sulphurous and metallic fumes of the Freiberg Metallurgical Works upon the vegetation of the surrounding fields. He found that plants were killed when placed in solutions containing oneoightieth per cent. arsenious acid, one-tiftieth per cent. sulphate of zinc, one-fortieth per cent. sulphate of copper, one=twentyfiftli per cent. sulphate of cobalt, one-tifteenth per cent. sulphate of nickel, and one-fifth per cent. sulph ate of iron. Mons. E. Heckel states that twenty five milligrams of arsenious acid, or the soluble arseniates in ninety grams of water, prevents germination and destroys the embryos of seeds. It is difficult, however, to agree with Prof. Freytag in the statement that the arsenious acid and the oxides of zinc and lead can not be injurious to vegetation on account of their prop erty of forming insoluble compounds in the soil, since in some of my preliminary experiments presence of such insoluble compounds as the arseniates of barium, strontium, and magnesium was sufficient to prevent germination. Again, in reports upon the composition of certain mineral waters of Germany, we notice statements of the presence of such insoluble compounds as arsenite of iron in solution. These facts argue against the possibility of accumulation of sufficient arsenic in the soil by regular applications of Paris Green in the quantities recommended for the destruction of the Colorado potato beetle. When rotation of crops is observed, and application of the poison can not therefore take place upon the same plot more than once in three or four years, it is probable that each application, being acted upon by the natural solvents in the soil, will be removed by drainage before another is made.
And yet, even when annual applications have been made, so much time must elapse before the limit could be attained that no injury need be feared from this cause. Now, can arsenic be absorbed and assimilated by the plant in the economy of growth? Investigations, the chem ist says, give a negative reply. All of the plants grown, from the largest to the smallest, were examined by careful application of Marsh's test; yet he failed in any case to detect the presence of arsenic. Before making the test, the organic rnatter of the plant was destroyed by boiling it in hydrochloric acid with addition of potassic chlorate, and the solution filtered. He also care fully examined potatoes which had been sub jected to applications of Paris Green, and which were furnished from Delaware and Sandusky, O., and Chambersburgh, Pa., and failed in any case to detect the presence of arsenic. With these facts before us, and without considering what might be the result of a series of experi ments continued through a number of years, we must conclude that plants have not the power to absorb and assimilate from the soil compounds of arsenic, and that though arsenical compounds exert an injurious influence upon vegetation, yet this is without effect until the quantity present reaches: for Paris Green, about 900 pounds per acre; for arsenite of potassa, about 400 pounds per acre; for arseniate of potassa, about 150 pounds per acre. The influence of illuminating gas upon the aerial portions of plants, is shown to be as follows: The subject of the influence of illuminating gas upon vegetation has, until within a short time, been neglected. In 1873, observatiOns made in Berlin determined the fact that gas escaping from the pipes exerted an injurious influence upon the surrounding vegetation, with the roots of which it came in contact, and careful experiment showed that this effect could be observed when so small a quantity as twenty-five cubic feet per diem was distributed through 144 square feet of soil to a depth of four feet. In fact, the plants whose roots permeated this quantity of soil, 576 cubic feet, were by such treatment killed in a short time, and it appeared that less tinie was'required to produce this effect when the surface of the ground was closed and more compact During the same year, J. Boehm made experiments by passing coal-gas through the soil of pots contain ing fuchsia and salvia; of the ten plants experi mented upon seven died in four months. Further experiments convinced him of the fact that the plants were killed, not by the direct action of the gas upon the roots, but by poisoning the soil. It seems, therefore, pretty well established that when coal-gas permeates through the soil it has an injurious action upon the vegetation with which it may come in contact. My attention has, however, been attracted to a somewhat dif ferent action of the gas, which seems equally as destructive as that .just described. Boehm found, in the course of his investigation, when cuttings. of willow were placed in bottles containing a small quantity of water, and otherwise filled_ with illuminating-gas, as the buds developed_ and the leaves began to appear the latter rapidly withered and died before reaching complete development. Now, this is the direction taken in my investigation. In Boehm's paper, lie does not state the percentage of gas in the atmosphere necessary to produce the effect described, and my object was therefore, if possible, to estimate the approximate quantity of gas required to. bring about such results. The question arose out of a dispute concernins the destruction of an extensive stock of camellias in Philadelphia, in which it was alleged that the loss was due to the escape of gas from the street-mains. It was shown that the main was broken; that during the winter, the ground being frozen, there was no means of escape of the gas other than to work its. way through the subsoil.. and into the atmos phere through the ground of the interior of Lhe greenhouse. The distance between the main and the greenhouse is not stated, but it appears that trees growing between the former and the latter were completely killed. It was to determine whether the result in dispute could be effected by the action of the gas. The plants were grow ing in pots placed upon stands and it was there fore impossible that they should be injured through the medium of their roots. It was then to determine what might be the influence of the gas in question upon the aerial portions of plants that the investigation about to be described was instituted. In order to secure such conditions. that the plants might be confined in an atmos phere containing a given quantity of gas, and yet be provided with the requisite degree of light, heat, and moisture, the plants were placed in closed boxes, provided with glass sides, the joints of which were cemented with white lead. When all was secured, a tube of glass was introduced_ through the side of the box and connected with the stop-cock of a gasometer. The stop-cock of the gasometer was then opened, and the gas allowed •to flow into the box, until the entire contents of the former were transferred to the lat ter. The whole was then allowed to stand until the following day, when the gasometer was again filled with gas taken from the pipes supplying the laboratory, and one-half the contents trans ferred to the box. On the next day, press of other duties called my attention away from this work entirely, and the box therefore received no gas. On the fourth day, however, one-half the contents of the gasometer were introdueed, arid another day allowed to intervene before another application. Gas was then introduced into the box on four occasions, so that the amounts trans ferred, allowing ten gallons for the capacity of the gasometer, were: February 24, about ten gallons; 25th, about five gallons; 27th, about five gallons; March 1, about five gallons. During this time, an occasional leaf, as well as one of the buds, fell from the plant, and on March 2, on opening the box to apply water to the plant, a slight jar caused a number of the leaves to fall. The plant was theu carefully removed from the box, when a sharp shock caused nearly all the leaves to fall. The leaves which had fallen were then gathered about the base of the plant, and the whole placed in a convenient position, together with the other plant, which had been submitted to the sarne conditions excepting the treatment with gas, and which remained perfectly sound and healthy. Now, what was the rela tive amount employed? The dimensions of the box were : horizontal cross-section, two feet square; height, four feet. Calculating from the data at hand, we find that the amount first introduced was equivalent to about 7.7 per cent. of the entire vol ume of the box, and that the quantity subsequently introduced, being one-half this amount, was but 3 35 per cent. Without making any allowances for escape of the gas by diffusion, which probably took place, reasoning from the fact that when the box was opened no odor of gas was percep tible within the box, we find that after the first day the amount of gas did not exceed four per cent. of the volume of the box. It is, however, 'probable that the average quantity was much less than three per cent., and I am inclined to the opinion that if camellias or other plants be confined in an atmosphere containing continually one to two per cent. of illuminating-gas, they must suffer and ultimately be killed.