CONTACT STIMULATION 



GEORGE E. STONE 



Amherst, Massachusetts 



The experiments presented here have been carried on since 1904, 

 at which time the writer observed some rather remarkable stimulated 

 growth responses induced in sunflowers when surrounded by wire 

 netting. At the time these observations were made we were carrying 

 on investigations relative to the effect of varying atmospheric electrical 

 potentials on plant growth, and for this purpose we made use of sun- 

 flowers established in large earthen pots or wooden boxes located at 

 different elevations in the open air. In some of these experiments 

 the plants were surrounded with wire netting and in contact with 

 the same but not with the soil, while in others (normals) no wire 

 netting was used. In some instances the wire netting was not only 

 in contact with the plants, but with the soil in which the plants were 

 growing; the soil being grounded by the use of copper plates in the 

 bottom of the boxes and by insulated wire, which led to the earth. 

 In other instances the plants were in contact with wire netting and 

 the soil, but were not grounded. The problem under consideration 

 at that time, however, more particularly concerned itself with the 

 influences of atmospheric electricity on plant growth, for which 

 purpose organisms of various kinds, including bacteria, were exposed 

 to elevations varying from thirty to sixty feet. Some of the earlier 

 experimenters have maintained that when plants were grown in the 

 free atmosphere surrounded with wires, they failed to develop, and 

 would eventually die in consequence of being deprived of the bene- 

 ficial effects supposed to be derived from atmospheric electricity. 

 In passing we may state that we have never observed any remarkable 

 mortality among plants in consequence of their being surrounded with 

 wires even when the experiments were performed at more or less high 

 elevation above the ground, and under ideal conditions for determining 

 the effects of atmospheric electricity on vegetation. Moreover the 

 growing of plants in conservatories where the electrical conditions of 

 the atmosphere are quite different from those out-of-doors demon- 

 strates the fallacy of this idea. On the other hand, we found that 

 plants were greatly stimulated by wire enclosures, especially when 

 they came in contact with the plants, and also the same stimulation 

 was noted when plants were grown thickly together and the leaves 



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