Nature and Cause of the Potato Disease. 
319 
breaking up of the vessels, and that eventually, as the disease 
advances, all communication ceases, and the upper parts of the 
plant die. 
I shall now state the results of an examination of seven plants 
of this year's growth visibly affected with the disease, and identical 
with that of the last season. 
These plants were forwarded to me by a gentleman of great 
practical knowledge, and better specimens for the purpose could 
not be desired. The stems were all connected with the parent 
sets, so that I had foliage stems, young tubers, roots, and sets 
complete. The upper part of the stems and leaves of the diseased 
plants had the dull and heavy appearance so characteristic of the 
disease ; and nearly the whole of the stems were more or less 
affected at one or other of the joints whence the lateral branches 
sprang from. In some of the plants the stem was most affected 
at a particular joint, in others the smaller branches and leaves 
were the most injured. No trace of fungi or insect was discover- 
able in some of the affected stems beyond the immediate localities 
of the diseased joints. The disease in those cases had not ex- 
tended itself, and was confined to a space not exceeding one inch 
of the length of the footstalk. In other cases the disease had 
spread both ways for a considerable distance from the wound, 
confining itself chiefly to the medulla. Fungi of the boleti and 
stellate kind were observable in all the diseased stems ; and at 
the parts where putrescence existed the eel-like animalcula 
abounded. The stem of one of the plants was hollow, the me- 
dulla having apparently lost its vitality, and died away. The 
hollow part extended to about three quarters of the length of the 
stem, from the root upwards. On examining the stem by thin 
transverse and longitudinal sections, I observed . that the vessels 
which traversed the Avails of the cells were filled with a rich brown 
coloured fibrous mass, the form of which could only be distin- 
guished at the angles of the cells severed by the cutting. The 
vessels also contained fungi of a similar colour to the fibrous mass, 
arranged in a star-like form ; these masses of fungi had pierced 
the walls of the cells in some instances, and appeared approach- 
ing their centres. The colour of the fungi imparted a tinge to 
the cells, so that the most diseased ones appeared brown. Plate 1 
represents the fibrous mass at the angles, and also the stellate 
fungi, as seen in the cell and vessels. 
One of the plants contained two diseased and one sound stem ; 
the stems were attached to the sets, and young tubers were formed 
on some of the stolons. 1 dissected the whole of the steins, and 
traced them microscopically downwards to the parent set ; the 
two diseased stems sprang from separate germs : one of them from 
the crown or principal eye, and the other from an adjoining lateral 
