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SECTION OF VEGETABLE PATHOLOGY. | OLD 
- 13.—THE POWDERY MILDEW OF THE GOOSEBERRY.* 
Spherotheca mors-uve, B. and C. 
(Plate XI.) 
(a) GENERAL REMARKS UPON THE GROWTH AND DEVELOPMENT OF THE POWDERY 
MILDEWS. 
The mildew that has proved so destructive to the gooseberry in- 
dustry in the United States, is a member of a group of fungi known 
to botanists as the Erysiphece. The species of this group are mainly 
parasitic upon higher plants, and several of them rank among the most 
injurious of suns to cultivated crops. The family, according to Sac- 
cardo,t is divided into nine genera, embracing a hundred species, 
about half of which are found in this country. ~ 
Among the leading species preying upon cultivated plants is Po- 
dosphera tridactyla, DeBy. Thisis often abundant upon the leaves 
and twigs of cherry, plum, and young apple trees, and does much dam- 
age in some localities. Phyllactina suffulta, Sacc., infests many 
species of forest trees, as the oak, beech, birch, ash, and catalpa. 
netnula salicis, Winter, is common upon willow leaves, while U. 
circinata, C and P., does much injury to the maple, especially the 
seedling plants. Last autumn it was difficult to find a young soft 
maple that did not have its leaves badly affected with this mildew. 
U. spiralis, B. and C. (U. Americana, Howe) is the Powdery mildew 
of the grape, fully treated in Bulletin No. 2, Botanical Division, pp. 
18-28. Other species of the genus Uncinula grow upon our Virginia 
creeper, mulberry, linden, poplar, and elm. The large genus Micro- 
sphera is well represented in the United States. The species upon 
the lilac, M. alni, Wint. (MZ. Friesii, Lev.), is perhaps the most com- 
mon. It infests the birches and buck-thorn in Europe, but does 
not thrive there upon the lilac. Other species are found upon the 
honeysuckle, buttonwood, oxalis, elder, dog-wood, oaks, beeches. 
and other hosts. The genus Hrysiphe is the largest in number and 
has a fair share of itssmembers in this country. LH. cichoracearum, 
DC., flourishes upon many composite, and may prove injurious to 
cultivated members of this great Sunflower family of plants. The 
most troublesome species is 7. communis, Fr. Lev., which infests all 
parts of the cultivated peas, often doing mnch injury. Grasses are 
frequently attacked by members of the genus ae and become 
coated with a whitish powdery mildew. June grass is a favorite sub- 
jectformildew. Hrysiphellais a genus with a single known species 
which preys upon the flower clusters of the alder, giving them a 
mealy appearance. 
The members of the whole family are much alike in their vegeta- 
tive condition, and differ principally in the structure of their sporo- 
+ carps, or cases for bearing their several spores. These mildews are 
all filamentous fungi that attack the host only upon its surface and 
give to the exterior a whitish or powdery appearance. It is on ac- 
count of this prevailing mealy or flour-like coating that the common 
name of ‘‘Powdery mildew” has been given to the members of 
this group. Theslender filaments of the fungus may become at- 
tached to the surface cells of the host by short irregular outgrowths 
*By Dr. Byron D. Halsted. + Sylloge Fungorum, Vol. I, 
