136 



PHYSIOLOGY OF NUTRITION. 



binding screws of the slide. The Rheotome (generally a magnetic 



hammer) with which 

 the primary coil is 

 usually provided is 

 not represented in 

 Fig. 46. For the 

 generating element 

 FIG. 46.-induction apparatus. we may employ the 



Bichromate cell represented in Fig. 47. 



The bottle contains a solution prepared by gradually adding 

 92 gr. of powdered Potassium bichromate to 93'5 c.c. of concen- 

 trated Sulphuric acid, and dissolving the mass in 900 c.c. of 

 water. The zinc plate can be lowered between the carbon plates, 

 or, when not in use, raised out of the fluid by means of the rod 

 carrying the binding screw. 



In investigations with the leaves of Elodea canadensis, I found 

 that weak induction currents arrested the 

 movements of the< protoplasm of the 

 cells ; on cessation of the current, the 

 movement gradually began anew. Strong 

 induction currents permanently arrested 

 the protoplasmic movements of a cell. 

 Since stronger currents kill the cells, and 

 the death of the protoplasm is readily 

 indicated by the fact that it becomes 

 permeable to many substances (e.g. pig- 

 ments) which it does not allow to 

 traverse it when living, it would be 

 instructive to allow electric stimuli to 

 act on hairs from the staminal filaments 

 of Tradescantia. The death of the cells would be at once 

 demonstrated by the escape of the pigment from the cell-sap 

 and from the cells. In studying the effect of electric currents 

 on plant cells, we notice also the changes of 'form that the pro- 

 toplasm suffers under the influence of the current.* It is further 

 instructive to make the following experiment : 8 We lay on a 

 sheet of glass two strips, each a few centimetres in length, from 

 a leaf of Begonia manicata. Through one piece of leaf we now 



* In investigating the influence of electricity on plants, we must further 

 take care to use unpolarisable electrodes, or the results will be vitiated. Ee- 

 spectiug these, see 63. 



FIG. 47. Bichromate cell. 



