Electricity — Radium-, N-, and X-rays 



vegetable substances. Wood, leaves, seeds, bulbs, blot- 

 ting-paper, as well as coal, resin, and jet, could all take 

 photographs of themselves. The exposure varies from a 

 few minutes to eighteen hours, and the only necessity is 

 to make sure that the material is absolutely dry. He is 

 careful, however, to point out that this effect is probably 

 due not to radio-activity but to a vapour of resin. 12 



There is also a mystery connected with what are called 

 N-rays. These seem to be only produced by fresh and 

 living protoplasm, for when the plants have been chloro- 

 formed they do not give out N-rays. 13 



The botany of to-day contains therefore many in- 

 teresting problems in physics which still await a proper 

 explanation. 



1 Ewart. 2 Pollacci, Ewart and Bayliss, Plowman. 8 Stone. 



* Lowenherz. 5 Foulerton and Kellas. 6 Sigmund. 



7 Polacci. 8 Molisch, (Dorn, Baumann, Valentiner). 



9 Dauphin and Green, Koernicke, Dixon and Whigham. 

 10 Green. u Tommasina. 12 Russell. I3 Meyer. 



217 



