l-'nderground stem of potato, showing the isoUtetl gnngrenous blotches on t!i9 
stem, roots, cords, and tubers. 
or rather by a pernicious, state of the atmosphere; the effects of 
which, as amongst, animals, breaks out sometimes in one part and 
sometimes in anotlier. Owing to the extreme excitabiUty of the 
plant this season in consequence of the long drought succeeded 
by heavy rains, a second ami a third production of young tubers 
were formed like a string of beads — those of more recent forma- 
tion upon cords thrown out by those which were older (Fig. C). 
Yet the shoots fiom the youngest were very frequently diseased, 
while the older cords and tubers were to the eye perfectly sound, 
— so strong a tendency has this disease to show itself in uncon- 
nected blotches. The rapid or slow destruction of the haulm and 
foliage depends upon the same conditions as that of the roots and 
tubers ; sometimes it is effiected in twenty-four hours ; sometimes 
from potatoes left in the ground when taken up last July) I pulled up 
several of them, the foliage of which was without a blemish, and to my 
surprisc^oMwt/ the gangrenous blotches just forminri on parts of every root. It 
is quite certain therefore that the particular pait on which it breaks out 
is sometimes above and sometimes below the surface of the soil. 
