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THE STIMULATION OP PLANT GROWTH BY MEANS OF WEAK POISONS 



THE STIMULATION OF PLANT GROWTH 

 BY MEANS OF WEAK POISONS 



By Howard S. Reed 



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 

 algae and fungi. In 1897, Richards discovered the 

 stimulating eifects 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 algae. 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. Miani 

 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 infiuence 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 GriflBths observed very good 

 results when it was applied at the rate of 50 to 100 

 pounds per acre. 



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 MnS04 + 0.2g FeSO^ 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 mangainese 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 



