296 Existence of electric Currents 



the discs on glass supports, and taking care to supply 

 moisture as fast as it was removed by evaporation. In every 

 case, some of the seeds were allowed to germinate on a glass 

 plate, for the purpose of affording comparative results. In 

 the first experiment, the cotton was moistened with distilled 

 water, and seeds of the garden cress (Lepidium sativum) 

 were placed on its surface.* In the course of two or three 

 days, the radicles appeared on all three surfaces (i. e. copper, 

 zinc, and glass), of almost equal vigour and size in each. In 

 a very short time, however, germination continued with great 

 vigour on the copper, but had nearly ceased on the zinc sur- 

 face of the compound discs. The plantules on the latter gra- 

 dually withered up and died : those on the plate of glass 

 were tolerably healthy, but by no means so vigorous as those 

 on the copper surface of the discs. Seeds of the common 

 pea (Pisum sativum) afforded precisely similar results. On 

 examining with test-papers the cotton on the surface of the 

 zinc, it was found to be acid, and that on the copper alkaline. 

 As the water with which the cotton was moistened had been 

 previously distilled, the evolution of acid and alkali can only 

 be attributed to the decomposition of saline matter present in 

 the seed itself. For the purpose of ascertaining what sub- 

 stances were really set free by the action of the voltaic current 

 on seeds, M. Becquerel made an analysis of the water in 

 which some garden cress had been allowed to germinate 

 during two months on zinc and copper surfaces, and found it 

 to consist, in 100 parts, of 



Oxide of Zinc - - 0*0005 



Hydrochloric Acid - - 0*0007 



Soda - - - 0*0002 



Water - - - 99*9936 



I repeated M. Becquerel' s experiments, substituting mustard 



seeds (Sinapis alba) for those of cress or peas. I placed the 



mustard seeds on the zinc and copper surfaces of compound 



discs, placed in saucers, and kept constantly moistened with 



rain-water : the metallic discs were covered with flannel. The 



experiment commenced on April 14. The temperature of 



the room in which the saucers were placed was kept pretty 



constantly at 64°. 



April 17. Copper surface. Testae burst; cotyledons all sepa- 

 rated, radicles protruding about one-sixth of an inch. 



Zinc surface. Testae burst ; cotyledons scarcely sepa- 

 rated ; in most of the seeds the line of division only distinct, 

 radicles of very few protruding. 



* Becquerel, Traite de l'E'lectricite et du Magnetisme, torn. iv. p. 177. 



