22 Diseases of the Potatoe. 



show, that the disease arises from the vegetable power of the 

 sets planted, having been exhausted by over-ripening, so that 

 gets from the waxy end of the potatoe produced healthy plants, 

 whereas those from the best ripened end did not vegetate at 

 all, or produced curled plants. It is the opinion of Mr. 

 Crichton, that the curl in the potatoe, may often be occa- 

 sioned by the way the potatoes are treated that are intended 

 for seed. " I have observed," he says, " wherever the seed 

 stock is carefully pitted, and not exposed to the air in the 

 spring, the crop has seldom any curl ; but where the seed 

 stock is put into barns -arid not houses, for months together, 

 such crop seldom escapes turning out in a great measure 

 curled ; and if but few curl the first year, if they are planted 

 . again, it is more than probable the half of them will curl 

 again next year." 



Mr. Knight, on the subject of this disease, in an article 

 written in 1810, says : " A few years ago the curl destroyed 

 many of our best varieties of the potatoe, to the attacks of 

 which every good variety will probably be subject. 



I observed that the leaves of several kinds of potatoes, 

 which were dry and farinaceous, that I cultivated, produced 

 curled leaves, while those other kinds, which were soft and 

 aqueous, were perfectly well formed, whence I was led to 

 suspect that the disease originated in the preternaturally 

 inspissated state of the sap in the dry and farinaceous varieties. 

 I conceived that the sap, if not sufficiently fluid, might stag- 

 nate in, and close, the fine vessels of the leaf during its 

 growth and extension, and thus occasion the irregular con- 

 tractions which constitute this disease ; and this conclusion, 

 which I drew many years ago, is perfectly consistent with the 

 opinions I have subsequently entertained, respecting the for- 

 mation of leaves. I therefore suffered a quantity of potatoes, 

 the produce almost wholly of diseased plants, to remain in 

 the heap, where they had been preserved during winter, till 



