EFFECT OF INVISIBLE RADIATION AND EMANATIONS 619 



Response of Mimosa to electric radiation. — In the last 

 case, in order to subject the specimen to the intense action of 

 electric waves, the radiator was electrically connected with 

 the responding organ, which was diffusely stimulated by it, 

 and exhibited a longitudinal response of contraction. If, 

 however, we wish to observe the effect of the unilateral action, 

 it will be necessary that the radiation shall act on one side 

 only. A difficulty is here met with, however, owing to the 

 relatively greater length of these electric waves, which, like 

 those of sound, do not cast shadows, but curl round corners. 

 In order to produce unilateral action, then, the length of 

 these waves has to be reduced to a minimum. By using 

 small spheres of platinum as the source of radiation, I 

 succeeded in obtaining short electric waves of about i cm. in 

 length ; but the intensity of such radiation is somewhat 

 feeble, and with them I could only occasionally obtain 

 responsive curvatures of growth. I was, however, more 

 successful in obtaining responsive effects from the pulvinus 

 of Mimosa. When the small radiator which I have described 

 was placed at a distance of a few centimetres from the lower 

 half of a pulvinus, and when the radiator was allowed to act, 

 a depression of the leaf of this plant occurred after an 

 exposure of nearly half a minute to the continuous action. 

 It should be mentioned that for the demonstration of this 

 effect it is the younger leaves which are suitable, the older 

 not being sufficiently sensitive. With regard to the electric 

 waves, it is to be borne in mind that to them water is opaque, 

 while ebonite is highly transparent. Hence the interposition 

 of a sheet of ebonite, between the radiator and the plant, 

 does not stop the responsive action, while a parallel-sided 

 trough of water in the same place would effectually prevent 

 the passage of the rays, and thereby put an end to the 

 action. 



Action of high frequency Tesla current. Ifoncelcctrode 

 of a Tesla coil be put in connection with the growing organ, 

 this electric variation of high frequency is found to cause 

 an arrest of growth. Even the contiguity of wires carr)-ing 



