THE STIMULATION OF PLANT GROWTH BY MEANS OF WEAK POISONS That plant growth can be accelerated by the action of certain poisons has been known for some time. The method was at first practiced in labora tory cultures, but has now been applied success fully to plants growing in the field. Experiments indicate that the tillers of small farms and market gardens would profit greatly by the practice of crop-stimulation ; they will be able not only to raise larger and more succulent vegetables but to hasten the maturity of them.
In the practice of medicine it is well known that when small doses of poison (e. g., strychnine, alcohol, arsenic) are administered, a stimulation of some part of the body results. In a general way, the same principle has been noticed in the growth of plants. The application of gypsum, or land plaster, while it undoubtedly sets free potash in the soil, has long been recognized as stimulating. The application of fungicides, as Bordeaux mix ture, has been found beneficial : first, the mixture kills parasitic fungi ; and, second, it stimulates the plants to more vigorous growth. Grapes and goose berries sprayed with Bordeaux mixture were found to contain 1 to 2 per cent more sugar than the fruit from unsprayed but healthy plants.
Experiments with poisons.
Experiments in pure cultures have been con ducted principally on the lowly plants, viz., the algm and fungi. In 1897, Richards discovered the stimulating effects of zinc salts on the growth of the mold fungi. Ono, working in Japan, found that compounds of zinc, copper and iron, when present in very small quantities, exerted a stimulating effect on the growth of algm. In this case he found that the stimulation was more manifest in the reproductive activity of the plants than in the growth in size of the individuals. Le Renard found that the greatest stimulation with mold fungi oc curred in the presence of the best and most avail able food supply. As supplementary to this fact, we may mention that the presence of very small amounts of copper in distilled water is fatal to the growth of the roots of seedlings; while in the pres ence of food it would undoubtedly cause stimulation.
The writer has observed that seeds which have been soaked in very weak potassium bichromate solution to kill adhering germs, germinate in shorter time than those soaked in pure water. Aliani found, too, that pollen-grains germinated better in water containing copper coins than in pure water. The effect of chemicals on seed germination has been studied by many investigators, under a variety of conditions, and the literature is rather extensive. With the exception of certain reagents, however, no definite general statements can be made regard ing their action. Further work is needed to estab lish the principles on which action takes place. It is probable that the factors influencing germination differ fundamentally in certain respects from those affecting later growth. One need not expect, there fore, that germination will be stimulated by the same compounds that stimulate the growth of the adolescent plant.
Richards and his students have recently estab lished the fact that stimulated plants work more economically than unstimulated plants, i. e., they attain to a given size and weight with a much smaller consumption of food material.
The results obtained from growing plants in pure culture are not all applicable to plants growing in the soil. Compounds of iron, manganese, fluorin, and iodin seem to promise most for practical agri culture. The best results have often been obtained by applying a mixture of two or more compounds.
Sulfate of iron (copperas) has often been the subject of experiment. Some experimenters re ported favorable results, some unfavorable, and some inferred that it had no influence whatever. Its benefits varied according to the quantities used. Loew found that the application of 1 to 2 ounces of sulfate of iron per ton of soil resulted in a stimu lating action, and Griffiths observed very good results when it was applied at the rate of 50 to 100 pounds per acre.