SIDE LIGHTS ON THE POTATO DISEASE. 
159 
The study of the potato-fungus is by no means a simple 
matter, not only from its extreme minuteness, but from the 
number of other fungi which play a part in destroying the 
potato ; amongst the foremost of these fungi we may mention 
Acrostalagmus cinnabarinus (Corda), Torula herbarum (Lk.), 
JDactylium tenellum (Fr.), D. pyriferum (Fr.), Cladosporium 
herbarum (Lk.), Mucor mucedo (L.), M. ramosus (Bull), Asco- 
phora mucedo (Tode), Penicillium crustaceum (Fr.), P. candi- 
dum (Fr.), Stysanus stemonitis (Corda), Fusisporium betce. 
(Desm.), Volutella ciliata (Fr.), Papulaspora sepedonioides 
(Preuss), and various species coming under Sporidesmium , 
Vermicularia , Myrothecium , &c., &c. The task to discrimi- 
nate between one and the other of this set and many other 
allied species is no slight piece of work, and one not likely to 
be in the way of the competitors for Lord Cathcart’s prize. 
We do not propose here to enumerate the list of growers’ 
varieties, early and late, new and old, British and foreign, 
which are said to be able more or less to resist the disease, as 
the subject is involved and interminable beyond reason; for years 
past the pages of the 44 Gardeners’ Chronicle” alone have swarmed 
with experiments and results, counter-experiments and counter- 
results, without end. No doubt, if these communications were 
properly digested and tabulated, something valuable might be 
learned from the deductions they would show ; but at present 
nothing of the sort has been done, and all the data founded 
on the experience of trade growers are in chaotic confusion. 
So that our paper may not be like the play of “ Hamlet ” 
with the part of 46 Hamlet ” omitted, we will in as few words as 
possible describe the fungus which is said to be the undoubted 
cause of the potato disease. The spores of Peronospora 
infestans which fall upon the foliage of the potato are ovoid 
and transparent, the longest diameter being about gwo-th °f an 
inch, the spores being borne upon slender transparent threads 
not half the above diameter. Having fallen upon a suitable 
nidus, with favourable circumstances of humidity, the outer coat 
of the spores becomes ruptured, and the corrosive plasma which 
they contain is set free. This mycelium speedily penetrates 
the epidermis of the leaf and permeates the cellular tissue in 
every direction, destroying the cells, and ultimately sending out 
fertile branches through the breathing spores of the leaf into 
the air. These branches, which are swollen in a moniliform 
manner (probably owing to repeated abortive attempts to pro- 
duce fruit), terminate with spores at their extremities. How 
whilst the mycelium is traversing the leaf-stalks and stems 
and hurrying on to the tuber itself, to blacken and consume 
the starch, the free fungus is all the while producing its 
spores, and amongst the spores bodies of a larger size which 
