20 MR. BERKELEY ON THE POTATO MURRAIN. 



It is the combination of untoward circumstances that has done 

 the mischief." 



" It may be urged perhaps, in opposition to this explanation, 

 that potatoes thrive very well in districts whose summers are usu- 

 ally as unfavourable as this has been ; as for example the cold parts 

 of Scotland. And that is doubtless true. But in those climates 

 the potato grows slowly, its tissue becomes thoroughly organ- 

 ized as it proceeds, and it is not liable to be acted upon by ac- 

 cumulated moisture. There no predisposing cause exists. But 

 in England the potato was predisposed to take the disease 

 which is destroying it by the unusual warmth of the beginning 

 of July suddenly succeeding a period of cold, ungenial weather ; 

 at that time the temperature of the soil near London was 

 between 60° and 68° ; the potatoes grew excessively fast, their 

 tissue was soft and unconsolidated, filled with azotized matter, as 

 all such tissue always is, and peculiarly liable to run into a state 

 of rottenness." 



The most complete statement after this is in a pamphlet by Dr. 

 Vallez and De Potter. I have not been able to procure the 

 original pamphlet, but, by the kindness of Messrs. Desmazieres 

 and Decaisne, I have received extracts from the ' Moniteur 

 Beige ' of the 29th of August, and the Belgian ' Precurseur ' 

 of the 16th of September, 1845, which contain, evidently, the most 

 important portions of the pamphlet. It will be well to give an 

 abstract, as the matter is stated somewhat differently by these 

 authors. 



The earth at the commencement of June, they say, in con- 

 sequence of its dryness and the extreme heat with which it was 

 inundated, its low conducting powers and its negative state 

 of electricity, was necessarily a bad reservoir or general recipient 

 of the fluids just mentioned. 



The air, from want of rain, was also a bad conductor, and was, 

 in consequence, surcharged with electricity ; but great storms 

 suddenly took place : whilst the air got rid of its excess of elec- 

 tricity, and became, from its humidity, a better conductor, the 

 soil, from being a recipient of the moisture, was in a different 

 condition. It constituted a superficial sponge, in which all the 

 electricity contained in the air was absorbed, producing in it a 

 more violent action, and exciting a sudden and great in- 

 crea^^e of heat. In consequence of this condition, the tubers 

 became suddenly gorged with moisture, and the prey of putre- 

 faction. 



In whatever terms, in fact, from differences of climate or of 

 personal views, the matter may be stated, the exciting cause of 

 the decay is by all considered excess of moisture combined 

 more or less with heat, or electric agency. In addition to the 



