SILVA OF NORTH AMERICA. 
ROSACE. 
Prunus, the classical name of the Plum-tree, was adopted by Linneus for a section of the genus 
as now extended. 
cent Rosacee is very great, and as the fruit-trees of the temperate 
zones belong to this family, they have been more carefully studied. 
than those affecting any other family, with the exception of Vitacew. 
Of the fungi which attack the North American species of Prunus, 
one of the most striking is Plowrightia morbosa, Saccardo (Spheria 
morbosa, Schweinitz), which produces the warty excrescences known 
as Black Knot. These were formerly supposed to be due to the 
attacks of insects, but their fungal nature is now known (Farlow, 
Bull. Bussey Inst. i. 440, t.4, 5,6). Plowrightia morbosa is peculiar to 
North America, and is found on Prunus Americana, Prunus nigra, 
Prunus hortulana, Prunus angustifolia, Prunus maritima, Prunus 
subcordata, Prunus Pennsylvanica, Prunus serotina, and Prunus Vir- 
giniana. The ugly black knots which often cover the branches 
of these plants are familiar ; there are two forms of fructifica- 
tion, one called the conidial stage found in early summer when 
the surface of the knots is dark green, and the other ripening in 
midwinter or early spring when the knots begin to break up. Hor- 
ticulturally considered, the Black Knot is a serious pest, as it passes 
from our native species of Prunus to the cultivated Plums and 
Cherries of Old World origin. 
abandoned in some of the eastern states, owing to the ravages of 
The cultivation of Plums has been 
this fungus ; and in some parts of the country, varieties of cultivated 
Cherries are also badly diseased. The disease has been known for 
many years in the eastern states, but has not developed on the cul- 
tivated Plums and Cherries of California, although, as the fungus is 
endemic on the native species of the Pacific coast, it may be ex- 
pected to spread sooner or later to the fruit-growing regions of the 
coast. In Europe no native disease corresponds to Black Knot, 
which has not yet been imported from America. 
Next in seriousness among the diseases which affect our spe- 
cies of Prunus are the prominent deformities caused by species of 
Taphrina, which produce Leaf-curl. The most striking of these is 
Taphrina deformans, Tulasne, which causes the leaves of Peach-trees * 
to become thickened, curled, and wrinkled, doing, however, less real 
injury than the disease called The Yellows, the origin of which is 
not yet satisfactorily determined. The plant which by some authori- 
ties is considered a variety of Taphrina deformans (var. Wiesneri, 
Rathay) is occasionally seen on Prunus serotina, although the exact 
A similar dis- 
ease, Taphrina Pruni, Tulasne, causes the distortion known as Plum- 
determination of the species is not beyond question. 
pockets on cultivated Plums, and on the fruits of our native Prunus 
serotina and Prunus maritima, and of a few other species. The pock- 
ets are best seen in the cultivated Plums, which are attacked in 
early summer soon after the fruit sets; the young ovaries swell, 
often almost to the size of full-grown plums, by the latter part of 
June, when they are hollow with the exception of a few fibrous 
bands, and are white and powdery. Similar, although smaller, pock- 
ets are sometimes found on wild Plum-trees, and it is probable that 
the disease is a native of America as well as of Europe, where it 
is common. It should not be confounded with Monilia fructigena, 
Persoon, a mould-like fungus which attacks cherries, plums, and 
peaches as they ripen, covering them with a grayish powder without, 
however, causing them to become hollow. 
The leaves of the different species of Prunus are attacked by a 
The Rust, 
Puccinia Pruni-spinose, Persoon, causes small yellow or brownish 
number of small fungi, some of which are destructive. 
yellow spots to appear on the under surface, with accompanying 
purplish-red spots on the upper surface, of the leaves of Prunus 
serotina, Prunus Virginiana, and other species, as well as on those 
of the Peach and the Almond. In the southern states, especially, 
this Rust is common on Peach-trees, and is often accompanied by a 
thin white mould (Cercosporella Persica, Saccardo). 
The Mildew, Podosphera Oxyacanthe, De Bary, is widely dis- 
tributed in Europe and America on wild and cultivated species of 
Prunus, as well as on various species of Pomew. Other fungi which 
attack North American species of Prunus are Septoria cerasina, 
Berkeley & Ravenel, which forms destructive small black spots on 
the leaves ; Monilia Linhartiana, Magnus, which covers the leaves 
of Prunus Virginiana with a web-like moyld, causing them to dry 
and fall; the curious Cornularia Persice, Saccardo, which forms 
small black club-shaped bunches on the bark of Peach-trees ; and 
the cinnabar-colored Punk-fungus, Polyporus cinnabarinus, Fries, 
common on the native Wild Cherries used for fencing. 
