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 
sets 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. “Ihave 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 and not houses, for months together, 
such crop seldom escapes turning out mm 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 origiated 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 
