1, Leaf attacked by the fungus; 2, Fructification or _perithecium_; the
end of one of its numerous appendages is shown more highly magnified in
3, 4, 5, spore sacs (_asci_) from the _perithecium_, containing spores.]
A much more prevalent disease is that caused by _Microsphaeria
Grossulariae_. This is a mildew growing on the surface of the leaf and
sending suckers into the epidermis. The white mycelium gives the leaves
of the plant the appearance of having been whitewashed (fig. 2).
Numerous white spores are produced in the summer which are able to
germinate immediately, and later small blackish fruits (_perithecia_)
are produced that pass uninjured through the winter liberating the
spores they contain in the spring, which infect the young developing
leaves of the bush. In bad cases the plants are greatly injured but
frequently little harm is done. Attacked plants should be sprayed with
potassium sulphide.
[Illustration: From the _Journal of the Board of Agriculture_ (May
1907), by permission of the Dept. of Agriculture and Technical
Instruction for Ireland.
FIG. 3A.--American Gooseberry Mildew (_Sphaerotheca mors-uvae_). Plant
with leaves and fruit attacked by the fungus.]
An allied fungus, _Sphaerotheca mors-uvae_, of much greater virulence,
has recently appeared in England, causing the disease known as "American
gooseberry mildew" (fig. 3A). In the main the mode of attack is similar
to that of the last-mentioned, but not only are the leaves attacked, but
the tips of the young shoots and the fruits become covered by the
cobweb-like mycelium, the attack frequently resulting in the death of
the shoots and the destruction of the fruits. After a time the mycelium
becomes rusty brown and produces the winter form of the fungus. Through
the winter the shoots are covered thickly with the brown mycelium and in
the spring the spores contained in the perithecia germinate and start
the infection anew, as in the case of the European mildew. This fungus
has recently been the subject of legislation, and when it appears in a
district strong repressive measures are called for. In bad cases the
attacked bushes should be destroyed, while in milder attacks frequent
spraying with potassium sulphide and the pruning off and immediate
destruction by fire of all the young shoots showing the mildew should be
resorted to.
[Illustration: FIG. 3B.--1, Fructification (_perithecium_) bursting,
ascus containing spores protruding; 2, Ascus with spores more highly
magnified.]
The gooseberry, when ripe, yields a fine wine by the fermentation of the
juice with water and sugar, the resulting sparkling liquor retaining
much of the flavour of the fruit. By similarly treating the juice of the
green fruit, picked just before it ripens, an effervescing wine is
produced, nearly resembling some kinds of champagne, and, when skilfully
prepared, far superior to much of the liquor sold under that name.
Brandy has been made from ripe gooseberries by distillation; by exposing
the juice with sugar to the acetous fermentation a good vinegar may be
obtained. The gooseberry, when perfectly ripe, contains a large quantity
of sugar, most abundant in the red and amber varieties; in the former it
amounts to from 6 to upwards of 8%. The acidity of the fruit is chiefly
due to malic acid.
Several other species of the sub-genus produce edible fruit, though none
have as yet been brought under economic culture. Among them may be
noticed _R. oxyacanthoides_ and _R. Cynosbati_, abundant in Canada and
the northern parts of the United States, and _R. gracile_, common along
the Alleghany range. The group is a widely distributed one in the north
temperate zone,--one species is found in Europe extending to the
Caucasus and North Africa (Atlas Mountains), five occur in Asia and
nineteen in North America, the range extending southwards to Mexico and
Guatemala.