The advantage of applying two stimulating sub stances to the soil instead of one may be seen from the results of an experiment which Loew performed, using tobacco plants. The plants were grown in soil in pots, some were watered with dilute solutions of manganous sulfate and iron sul fate (0.3g ± 0.2g in 100 cc. water), others with manganous sulfate or iron alone. The average height to which the plants attained in eleven weeks after the application of stimulants was as follows : When no stimulant was applied, 45 inches ; when manganese and iron were both applied, 59 inches ; when manganese alone was applied, 58 inches ; when iron alone was applied, 55 inches. The average number of flowers and buds on the same plant was also distinctly greater on the plants that received two stimulants. Those that received both manganese and iron produced 63 flowers and buds ; when manganese alone was applied there were 50 ; when iron only was applied there were 55, and on the control plants, none. It is thus shown that the application of stimulants not only produced larger plants, but hastened their period of blossoming. An additional point in favor of iron sulfate and manganous sulfate is their cheapness, since both salts can be applied directly in the raw, unpurified state.
Compounds of iodin have given marked stimu lation to plant growth. However, since they are extremely poisonous to plants, they must be used in very small quantities. A top-dressing of iodid of potassium, applied at the rate of 50 pounds to the acre, injured wheat and barley. Suzuki found that such small quantities as one-third of an ounce per acre were sufficient to cause stimulation, and that four ounces per acre was amply sufficient. These small quantities were dissolved in water and sprinkled on the soil. This substance increased the weight of radishes 31 per cent over the yield on control plots.
The writer has tried the effect of some poisonous substances on the growth of potatoes. Although the results are far from complete, they indicate that magnesium carbonate, applied at the rate of 200 pounds per acre, and iron and manganous sul fate applied at the rate of 17 and 175 pounds per acre respectively, exert a stimulating action on the growth of potato tubers. The benefits of stimu lation were shown not only in the increased yield of the tubers, but also in their improved quality.
The action of the same poisonous compound is not always the same on different crops, just as the feeding of different crops must vary. Thy action will probably vary also on soils accord ing to their content of acids or alkalies.
The application of small quantities of organic substances having a toxic effect at high concentrations is often beneficial, especially when applied to certain un productive soils. Bulletin No. 28 of the Bureau of Soils of the United States De partment of Agriculture describes the beneficial effects of tannic acid and of pyrogallol when applied in small quanti ties to an unproductive soil. The applica tion of tannic acid at the rate of one part per million of soil increased the growth of wheat seedlings about 75 per cent. In another experiment, pyrogallol was added at the rate of 500 parts per million of soil. On soil so treated, the growth of wheat plants was twice that on the un treated soil. While it is not probable that the application of either of these last named substances will be profitable for the commercial grower, it is shown that growth may be accelerated by a wide range of substances.
Etherization.
It may be in place to mention the action of anes thetics on plant growth, since the anaesthetics behave as poisons if they are allowed to act for any length of time. The plants are inclosed in a tight compartment and exposed for a short time to the vapors of ether or chloroform. At the Government Botanical Garden in Dresden, lilacs treated with ether on October 19 produced blossoms November 8. Another season the etherized plants blossomed November 13. Etherization does not hasten the blooming period of lilacs if the period of rest is entirely completed before the anaesthetic is applied.
The practice of etherization is meeting with favor among the florists of France. In America it has been applied with success to the forcing of rhubarb and asparagus. Sandsten showed that chlo roform and ether had an accelerating influence on seedlings, but they were injurious to narcissus.
Experiments made at the Cornell (N. V.) Experi ment Station gave interesting results. A Persian lilac, Syringa rulgaris, was placed in the forcing house on November 24, after having been etherized for 24 hours. Within five days many leaf-buds were entirely open, and by December 11 the plant was in full leaf: The first flower-buds opened on December 6, and the plant was in full bloom on December 25, just 31 days after the beginning of the experiment. A check plant did not reach full bloom till six days later. When the plants were exposed to ether fumes for a longer period, more marked results were secured. A lilac etherized for 48 hours made a gain in coming to full flower of 8 days over the check plant ; one etherized for 72 hours gained 10 days. Astilbe Japonica etherized for 24 hours, in one instance was in full bloom a month to five weeks before the check plant. Experi ments with bulbs also showed favorable results from etherization (Fig. 47). Narcissus showed a gain varying from two days to three weeks in coming to full bloom, results contradictory to those secured by Sandsten. Two lots of Lilium longi forum showed a decidedly taller growth, but no gain in the time at which first blossoms appeared. A third lot, which had been etherized for a longer time, showed a gain in both time and height. [A brief account of these Cornell Experiments, by J. Eaton Howitt, and Claude I. Lewis, appears in The Cornell Countryman, May, 1906; a bulletin of the work has not appeared as this article is written.] Literature.
The following references include most of the liter ature that has been published on plant stimulation : Raulin, Etudes chimique sur la vegetation, Ann. d. Sci. Nat. Bot. [v] XI. 91, 1869; Richards, Die Beeinflussung des Wachstums einiger Pilze durch chemischer Reize, Jahrb. wiss. Dot. 30, 665, 1897 ; Sandsten, The Influence of Gases and Vapors on the Growth of Plants, Minn. Botanical Studies, Vol. 2, p. 53, 1898; Richards, The Effect of Chemical Irrita tion on the Economic Coefficient of Sugar, Bulletin, Torrey Rot. Club, Vol. 26, 463,1899; Ono, Lieber die Wachstumsbeschleunigung einiger Algen and Pilze durch chemischer Reize. Jour. College, Science, Imperial University, Tokyo, Vol. 13, 141-186, 1900; Loew, On the Treatment of Crops by Stimulating Compounds, Bul. College Agriculture Imperial Uni versity, Tokyo Vol. VI. 161-175, 1904 ; Latham, Stimulation of Sterigmatocystis by Chloroform, Bul. Torrey Bot. Club, Vol. 32, 337, 1905.