Nature and Cause of the Potato Disease. 
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1 A and 3 a are diseased at the germs, and 4 a is diseased in the 
vessels of the section, but the germ itself is uncontaminated. 
2 A and 3 a would, if they germinated, produce diseased plants ; 
4 A might produce a sound one, even if the whole section was 
used for seed j but if the affected part in 4 A was cut off at the 
diameter e c, thus getting rid of the apex of the angle containing 
the diseased portion of the section, a healthy plant might be de- 
pended upon as the effect of the germination of the gem. I do 
not connect the fact of a diseased germ generating a diseased 
plant with the disease of last season, but I consider it important 
to show that diseased tubers may generate diseased plants, be- 
cause it is highly probable that disease to some extent may exist 
in the present season, in consequence of the tubers of the last 
being so much affected, and especially so should the weather 
prove unfavourable during the growth of the tubers. 
Description of Drawings. 
No. 1 is the cell of a tvansveise section of a diseased stem from a joint 
in this season's plant. The brown circular spots are radiated fungi ; the 
insects, eel animalcule ; and the brown parts marked b are a continuation 
of the diseased vessels of the cells. The parts marked a are portions of 
the adjoining cells. 
No. 2 represents a longitudinal section of a diseased tuber ; a a A are 
gems ; b is the runner, or stolon. The yellow lines show the course of the 
vessels; the crimson, the extent of the disease. 
No. 3 represents a young plant growing from the set ; 1 is the set ; 2 
are Ihe stolons ; and 3 the roots. 
No. 4 is a transverse section of a diseased tuber ; 1 is the bark ; 2 
cuticle ; 3 reservoir of empty cells, that are always found beneath the 
cuticle ; 4 channels leading to the gems, and in which they are seated; 5 
diseased ; and 6 sound cells. 
No. 5 represents the vessels of the gems and the termination of the 
roots ; 1 is a germ, and 2 b are the spongiole of the roots ; the part b 
being the mouths of the absorbents. 
No. 6 is a longitudinal section of the stem of a young plant, and the 
part of the set Irom which it sprung; a, with crimson spots, represents a 
diseased part of the set or seed ; b the channel of the gem ; c cells of the 
set; D termination of the vessels of the gem in the channel of the set ; k 
the crown of the set, and 1 a and 2 a stolons ; 1 is the cuticle : 2 per- 
forated vessels with hexagonal perforations ; 3 vascular system, with dia- 
phragms ; 4 annular vessels ; 5 spirals, and b 6 the cellular arrangement 
of the medulla. 
No. 7 represents three kinds of fungi generated in diseased potatoes, 
plants, and other substances as well ; 1 a are short white fibrous fungi, 
found in substances before putrefaction, and sometimes afterwards, when 
a moderately dry surface is formed for them ; 1 b are round-headed boleti 
fungi; 3 is the same much magnified; 2 is radiated fungi, seen also in 
plate 1 ; 4 is radiated fungi, as seen growing from the vessels of the potato 
plant ; 5 is a head of the boleti crushed, for the purpose of examining for 
seed ; a is not seed, but air, enclosed in a film of water. 
No. 8 is a cell found in a transverse section of a diseased stem, of this 
year's growth, at the base where it joins the set or seed. It is infested 
with the botritis or grape-like fungi. 
2 a 2 
