ound when the _Peronospora_ is sown in a nourishing plant. The most
scrupulous examination demonstrates the most perfect identity between
the cultivated and spontaneous individuals as much in the organization
of the parasite as in the alteration of the plant that nourishes it.
In the experiments that he had made he affirms that he never observed
an individual or unhealthy predisposition of the nourishing plant. It
appeared to him, on the contrary, that the more the plant was healthy,
the more the mould prospered.

We cannot follow him through all the details of the growth and
development of the disease, or of his experiments on this and allied
species, which resulted in the affirmation that the mould immediately
determines the disease of the tubercles as well as that of the leaves,
and that the vegetation of the _Peronospora_ alone determines the
redoubtable epidemic to which the potato is exposed.[d] We believe
that this same observer is still engaged in a series of observations,
with the view, if possible, of suggesting some remedy or mitigation of
the disease.

Dr. Hassall pointed out, many years since, the action of fungous
mycelium, when coming in contact with cellular tissue, of inducing
decomposition, a fact which has been fully confirmed by Berkeley.

Unfortunately there are other species of the same genus of moulds which
are very destructive to garden produce. _Peronospora gangliformis_, B.,
attacks lettuces, and is but too common and injurious. _Peronospora
effusa_, Grev., is found on spinach and allied plants. _Peronospora
Schleideniana_, D. By., is in some years very common and destructive
to young onions, and field crops of lucerne are very liable to attack
from _Peronospora trifoliorum_, D. By.

The vine crops are liable to be seriously affected by a species of
mould, which is but the conidia form of a species of _Erysiphe_. This
mould, known under the name of _Oidium Tuckeri_, B., attacks the vines
in hothouses in this country, but on the Continent the vineyards often
suffer severely[e] from its depredations; unfortunately, not the only
pest to which the vine is subject, for an insect threatens to be even
more destructive.

Hop gardens suffer severely, in some years, from a similar disease; in
this instance the mature or ultimate form is perfected. The hop mildew
is _Sphaerotheca Castagnei_, Lev., which first appears as whitish
mouldy blotches on the leaves, soon becoming discoloured, and
developing