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 _Sphærotheca Castagnei_, Lév., which first appears as whitish mouldy blotches on the leaves, soon becoming discoloured, and developing the black receptacles on either surface of the leaf. These may be regarded as the cardinal diseases of fungoid origin to which useful plants are subject in this country. Amongst those of less importance, but still troublesome enough to secure the anathemas of cultivators, may be mentioned _Puccinia Apii_, Ca., often successful in spoiling beds of celery by attacking the leaves; _Cystopus candidus_, Lév., and _Glæosporium concentricum_, Grev., destructive to cabbages and other cruciferous plants; _Trichobasis Fabæ_, Lév., unsparing when once established on beans; _Erysiphe Martii_, Lév., in some seasons a great nuisance to the crop of peas. Fruit trees do not wholly escape, for _Roestelia cancellata_, Tul., attacks the leaves of the pear. _Puccinia prunorum_ affects the leaves of almost all the varieties of plum. Blisters caused by _Ascomyces deformans_, B., contort the leaves of peaches, as _Ascomyces bullatus_, B., does those of the pear, and _Ascomyces juglandis_, B., those of the walnut. Happily we do not at present suffer from _Ascomyces pruni_, Fchl., which, on the Continent, attacks young plum-fruits, causing them to shrivel and fall. During the past year pear-blossoms have suffered from what seems to be a form of _Helminthosporium pyrorum_, and the branches are sometimes infected with _Capnodium elongatum_; but orchards in the United States have a worse foe in the "black knot,"[f] which causes gouty swellings in the branches, and is caused by the _Sphæria morbosa_ of Schweinitz.