104 The Poiatoe Plague. 
been, very nearly the same, in all the countries where the 
potatoe is grown, and, consequently, all the causes which pro- 
duce the disease, have been simultaneously in operation, 
everywhere. That the disease is not an epidemic, we know, 
because sound and unsound potatoes are grown upon the 
same field. I say that the causes of the disease lie where I 
have placed them, because in almost every instance where 
the treatment of the crop has been based upon this theory, 
there has been no rot. There are, of course, exceptions to all 
general rules, and exceptions may be named to this, but the 
ereat fact remains true, and it will be a demonstrated truth 
next year, by all who are careful in selecting land and pre- 
paring their seed potatoes. 
Now I lay it down as an incontrovertible fact that potatoe 
sets from a highly cultivated field, and from a large crop, are 
not proper for seed, and that sets from such a crop will in- 
evitably give a diseased product; it may not be visible the 
first year, or the second; but the tuber is diseased, and the 
disease will out. Ido not say that farmers should not strive 
for large crops, but merely that sets should not be taken 
from them. I cannot precisely state the law governing this 
fact, but it has been remarked by Professor Morren that the 
potatoe is not a root— only a branch; and if the Professor 
is correct, then an easy solution for it is at hand. The plant, 
by over-production, has exhausted its vital energies. And 
this would seem to be the true reason why sets from such a 
crop are not proper for seed. 
Over-Rirrnine. Another cause to which I ascribe the 
rot, is the planting of over-ripened sets. I believe it will not 
be contended for a moment that over-ripened sets have not 
generally been planted, neither will it be asserted that the 
produce from sets not over-ripened have been, to any general 
extent, affected by the disease. In some cases they have; 
but, then, it will be traceable to pre-existing disease, arising 
