SIDE LIGHTS ON THE POTATO DISEASE. 
151 
reliable knowledge of the subject, ignoring everything but dry 
facts — has recently been written for the 44 Journal of the Eoyal 
Agricultural Society” (vol. ix. p. 1), in about 150 lines, by 
Mr. Carruthers, the Keeper of the Botanical Department of 
the British Museum : to any one desiring a resume of all that 
is actually known, written in the fewest possible words, we 
commend this essay. 
To men of science, and indeed to most intelligent readers 
(thanks to the popular scientific publications of the day), the 
fungus itself is now almost as well known as the commonest 
wayside plant ; but for a complete comprehension of Pero- 
nospora infestans , and its habit of life, one not only requires 
to perfectly know this unit by itself, but all its immediate 
allies, and indeed most other fungi. Without this knowledge 
one is apt to give greater importance to certain facts in its 
life history than they deserve, and to ignore the greater im- 
portance of certain others because they may appear in them- 
selves to be trivial. 
We will pass by those writers, whose views must be worth- 
less, who persistently confuse 44 zoospores ” with 44 oospores ” 
(and even sclerotia), and who write as if one name was sy- 
nonymous with the other two. 44 Zoospores ” are, of course, 
those bodies found on the fruiting threads of Peronospora 
(formed within certain privileged larger spores, by a differen- 
tiation of their contents), and which, when set free, move about 
like animalcules by means of cilia; whilst 44 oospores” are- 
found on the mycelium (buried in the tissues of the supporting 
plant), and formed by the discharge of the contents of a body 
having anther-like qualities into another body, which bears an 
organism somewhat analogous with the ovule in flowering plants. . 
Sclerotia proper, which Peronospora infestans may or may not 
have, are really knots of densely compacted mycelium, probably 
formed by the mycelial threads of the fungus winding them- 
selves round and round each other in a knot-like fashion. Why 
the mycelium of certain fungi should possess this function it is--: 
difficult to say, but it is nevertheless a fact that the mycelium 
of many of the higher fungi invariably gets compacted in this: 
way. The potato fungus produces spores and zoospores, by 
which it propagates itself ; and most writers competent to 
form an opinion consider it highly probable that 44 oospores ” 
are also produced on the mycelium, because, though never 
yet seen in connection with the potato-fungus itself, these 
44 oospores ” are produced on the threads of other and allied 
species of Peronospora. It is also uncertain whether the 
mycelium gets compacted into the small knotty bodies called 
sclerotia ; but it seems reasonable to assume that during winter 
the fungus rests in the form of oospores or sclerotia ; or where 
