656 POTATO ROT. 



writer, embracing substantially all that has been said on secon- 

 dary and predisposing causes, by the most sensible writers, 

 while it confirms their suggestions and opinions. The similar- 

 ity in the views of all these writers, as far as they are expressed, 

 is a striking confirmation of their correctness. 



After many pertinent, but general remarks, by way of intro- 

 duction, Mr. Dawson proceeds to consider the nature of the 

 disease. 



1. The general difi"usion and simultaneous occurrence of the 

 disease over extensive regions, is a remarkable fact ; and the 

 exceptions arising from the differences of soil and other causes, 

 are also very instructive in suggesting remedial measures. 

 Some of these exceptions will be considered subsequently. 



2. The disease has usually attacked the crop at that stage of 

 the growth, when the tops are fully formed, and the formation 

 and filling up of the underground tubers are most rapidly pro- 

 ceeding. Yet early potatoes often pass this critical period in 

 safety, while those which are late are attacked ; showing that 

 the weather or temperature acts with, or against the predispo- 

 sition at this particular stage of growth, and modifies its influ- 

 ence. 



3. The disease has usually first made its appearance in the 

 leaves, and descended from these to the stems or roots. The 

 remainder, under this head, containing a minute description of 

 the whole process of the disease, better adapted to scientific 

 men than to common readers, is necessarily omitted. 



As to causes, two important truths, deducible from the facts 

 already stated, at once meet us. 



1st. A disease so general and widely spread, probably prima- 

 rily depends on some great, and generally operating, predispos- 

 ing cause. 2ndly. Nothwithstanding this, it is locally induced 

 or prevented by the action of a great number of secondary 

 causes, which favor or arrest its development, and which yet 

 cannot be considered as the primary causes of its appearance. 

 Let us inquire first, into 



2. The inducing or secondary causes of the disease, and rem- 

 edies or palliatives founded oti their study. 



Most of these causes it will be necessary merely to name, as 



