POPULAR SCIENCE REVIEW. 
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consisting of a minute mould, proceeding, either singly or in fascicles, from 
the stomata, and arising from an abundant branched mycelium creeping in 
every direction through the loose tissue beneath the cuticle. The upper 
surface rarely, if ever, exhibits the mould, it being almost physically impos- 
sible for its delicate threads to penetrate the closely-packed cells which, 
being arranged side by side, leave scarcely any intercellular passages. The 
mould, in a few hours from its first piercing the apertures of the stomata, 
perfects its fruit, and in so doing completely exhausts the matrix, which in 
consequence withers. No sooner have a number of the leaves been attached, 
than the stem itself is subject to change, becoming spotted here and there 
with dark brown patches, in which the cells are mostly filled with a dark 
grumous mass, without exhibiting any mucedinous filaments ; though, 
occasionally, I have ascertained their presence. Very rarely fructifying but 
dwarfed specimens of the mould occur upon it. The stem now rapidly 
putrifies, the cuticle and its subjacent tissue becoming pulpy, and separating 
when touched from the woody parts beneath. The whole soon dries up, and 
in many instances exhibits in the centre the black, irregular fungoid masses 
which are known under the name of Sclerotium. varium , and which are be- 
lieved to be the mycelium of certain moulds in a high state of condensation. 
If the tubers are now examined, the greater part will often be found 
smaller than usual, especially if the disease has commenced at an early stage 
of growth ; but in their natural condition, while here and there a tuber, parti- 
cularly if it has been partially exposed, exhibits traces of disease. The 
surface is, however, soon marked with livid patches, commencing generally 
about the eyes, or at the point of connection with the fructifying shoots : 
these rapidly acquire a spotted appearance, the spots being rather waved, 
and assuming often a more or less concentric arrangement. Sometimes, — 
especially on the smoother kinds of tuber, — two or more regular systems of 
concentric spots are exhibited on the same tuber. The skin now withers, 
and is easily separated ; the spots become depressed and of a yellowish 
tinge ; and if the tubers be laid in a moist place, in a day or two — some- 
times in a few hours — the same mould which destroyed the leaves springs 
from them, piercing the cuticle from within, yet not scattered, as on the 
leaves, but forming a conspicuous white tuft. If a section of the diseased 
tuber be made on the first symptoms of the disease, little brownish or rusty 
specks are found in the cellular tissue, confined, with very rare exceptions, 
to the space between the cuticle and the sac, if I may so call it, of spiral 
vessels and their accompanying tissue, which springing from the subterranean 
branches, pass into the tuber, making their way to the several buds 
disposed on the surface. These spots consist at first of a quantity of dis- 
coloured cells, mixed more or less with others in a healthy condition. The 
grains of fecula are for a long time perfectly healthy ; the cells themselves, 
so far from being looser, are more closely bound together than in the more 
healthy portions. The rusty spots soon exhibit a darker tint, spreading in 
every direction and becoming confluent ; they at length extend beyond the 
barrier of vascular tissue, and attack the central mass. The tuber, mean- 
while, assumes a disagreeable smell, decomposes more or less rapidly, other 
Fungi establish themselves on the surface, or in the decaying mass, which 
cniits a highly fetid odour, resembling that of decaying agarics, the union of 
