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4. Diseases. 



All other disorders to which potatoes are liable, are overlooked in 

 the presence of the modern rot. A disorder so widespread and so 

 destructive has of course attracted the attention of practical and 

 scientific men in many countries ; and all the resources of learning 

 and skill have been applied to the investigation of its causes and its 

 remedies, hitherto with small success. At least, thej have only 

 shown, not what the cause is, but what it is not. The universality 

 of the evil proves that it could not have been occasioned by blight, 

 insects, climate, or eoils ; for it is not to be supposed that these Avere 

 evci-ywhere, and at the same time cooperating to one end. Besides, 

 these causes existed long ago, and did not produce the results we 

 now witness. As to insects and fvxngi, they may be regarded rather 

 as effects, than as causes of the disease. A true theory must account 

 for all phenomena, and a true remedy reach all similar cases. In 

 both points, recent researches have signally failed ; and from various 

 quarters we learn that investigations are abandoned in despair of 

 attaining a satisfactory solution of the difficulty. 



I am not disposed to increase the number of unsuccessful physi- 

 cians ; but shall only suggest a few thoughts respecting the proximate 

 causes or aggravations of the disorder. I suppose they are nearest 

 to the right, who consider the continued propagation of the plant 

 without renewal from its original climate and soil, and its over-stimu- 

 lation by strong manure, as, at least, secondary or auxiliary causes 

 of its decay. We should not forget that the plant we cultivate is 

 not the original potato in its native home, where it doubtless preserves 

 its health from age to age, like other wild inhabitants of the forests. 

 Scarcely any foreign plant has been subjected to a discipline so 

 severe ; to methods of culture so different from what nature appointed 

 for this. For some purposes we have changed it for the better ; for 

 instance, in the quantity and quality of its tubers — making them not 

 only an abundant but palatable article of food. But this result may 

 have been attained at the expense of health. Not that the potato is 

 actually running out and is about to die. That seldom occurs to any 

 plants, and especially unlikely is it to occur to those propagated only 

 by seeds ; although they may and do degenerate to such an extent 

 as to render their cultivation unprofitable. And this process is 

 hastened by modes of culture d'.fferent from those by which the plant 

 naturally propagates itself. In its wild state, the potato produces 

 small tubers and long tops. We have increased the fruit and 



