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Ill
mCEOSCOPIC FUNGI.
plant, wliere they extend, ramify themselves, and
become a mycelium. This mycelium originates
branched threads, bearing acrospores at the tips
of Perono-
of their branchlets, and in many species
sijora another kind of reproductive body upon the
threads of the mycelium itself. To these bodies we
must briefly address ourselves.
This last kind of reproductive organs (not yet
positively found in the potato mould) appear to be
wholly analogous to the oogonia of the "white
rusts" already described, producing oospores in
like manner. Dr. de Bary avows with regret that
his numerous efforts to observe the germination of
these oospores were unsuccessful. Nevertheless,
he considers that the perfect resemblance between
them and the oospores of the " white rusts '' will
justify him in concluding that the germination in
both is
very similar. It will be unnecessary to
repeat
here the observations already made on the
growth and development of oogones and zoospores.
What has been advanced respecting these organs
in Gystopus will apply also to Peronospora.
Potato Mould.— Towards the close of the summer
of 1845, in the course of a few weeks, every
one became aware of the fact that a new disease
had appeared which threatened the entire destruction
of the potato crop. Until then it seemed to
have been almost, although not
entirely unknown.
about the
It first appeared in the Isle of Wight
middle of August, and a week afterwards had be-