50 RELATION OF THE DISEASE TO EXTERNAL CAUSES. 

 ELECTRICITY. 



(194.) Nothing is known of the influence of electricity 

 upon the growth of plants. The world was startled a year 

 or two ago by the notion that electricity was to serve the 

 purposes of manure ; there is no doubt, however, that the 

 author of this idea was mistaken. The influence of 

 artificial electricity upon plants is unknown ; and, in fact, 

 the artificial application of electricity has not been proved 

 to exert any influence whatever. To conduct experiments 

 on this subject would entail much labor and expense upon 

 the experimenter, but I believe they would be well worth 

 trying in a manner different from former experiments. 



HYGROMETRIC CONDITION OF THE ATMOSPHERE. 



(195.) Every plant requires a certain hygrometric con- 

 dition of atmosphere. Hence some plants, as ferns, require 

 a moist atmosphere ; other plants, the flowering plants for 

 instance, require an atmosphere which is dryer. 



(196.) Too much moisture prevents the woody fibre from 

 being perfectly ripened -, and the wet season of last year 

 has been assumed as a cause of the potatoe disease. This 

 year, however, has been especially the reverse, and yet 

 the disease continues or even increases. 



(197.) Moisture is not the cause of the disease, although 

 it may influence it. When the under-ground stems are 

 cut off by gangrene, a moist atmosphere will fill and swell 

 out the haulm with water, when a hot day subsequently 

 acting upon it will totally destroy it and cause it to rot. 



(198.) Potatoe tubers kept in a wet atmosphere I have 



