96 The Potatoe Plague. 



of climate, soils or manures ; warm or cold latitudes ; in hot, 

 dry, wet, and cold seasons ; under every possible feature of 

 cultivation, and in every condition of the crop, as managed by 

 all sorts of farmers, throughout the whole of this country and 

 all the countries of Europe. These facts remembered we 

 must discard the idea that atmospheric influences would pro- 

 duce the disease ; manures and soils could not produce it ; 

 excessive heat or cold could not affect the crop so universally. 

 The disease has been steadily increasing for years in defiance 

 of all the conditions that these various theories would estab- 

 lish as governing the malady. They are partial in their 

 operation, and must, therefore, be rejected as insufficient. 

 The cause of rot, says an intelligent writer, cannot be in the 

 soil, since AVC find healthy and diseased potatoes growing be- 

 side each other ; that is to say, on soils of the same constitu- 

 tion we sometimes find the rot in alternate plants, or in whole 

 rows. It cannot be attributed to the atmosphere, as all plants 

 and roots are equally surrounded by it ; nor can the cause be 

 in the manure, as all the tubers receive the same kind, and 

 nearly the same quantity. It must, therefore, be attributed 

 to the potatoe itself. 



We have, then, to consider the most popular theory, which 

 ascribes the disease to the influence of the growth of fungi. 

 This position is the one taken by the principal vegetable 

 physiologists of Great Britain and this country, and most of 

 the directions published in the agricultural papers are made 

 with reference to this fact. That this is not the true cause 

 of the disease, is, I think, made sufficiently clear by the con- 

 cluding paragraphs of the last chapter. That evidences of 

 the appearance of fungi have been discovered, and are dis- 

 coverable in all diseased potatoes, I do not deny, but I assert 

 that they are a consequence of disease and not the cause. 

 Liebig says in his Chemistry of Agriculture " The micro- 

 scopical examination of vegetable and animal matter, in the 



