376 REPORT OF THE COMMISSIONER OF AGRICULTURE. 
leaves and tips of the young canes of Ribes rotundifolia, Michx., are 
usually badly infested in Iowa, and last summer the writer found 
the half-grown berries of a wild gooseberry in Colorado, Ribes di- 
varicatum var. irriquum, Gray, so covered with the fungus as to 
preclude their perfect development. 
(c) EXTERNAL APPEARANCE AND ACTION OF THE FUNGUS. 
The mildew first makes its appearance upon the young half-grown 
leaves and the unfolding terminal bud of the shoot. Inits early stage 
it has a cobweby appearance which soon becomes white and powdery 
from the development of the light conidial spores. Soon after this 
thin patches of the same character may be found upon the forming 
berries. Usually one side is more attacked than the other, and as 
the berry continues to grow it becomes one-sided or curved, because 
the fungus retards the development upon the infested side. If the 
berry is entirely covered its further development is generally checked. 
Later in the season the leaves, and especially their petioles and the 
young stems bearing them, turn to a rusty-brown color and become 
thickly coated with the fungus. The berries at the same time are 
covered with brown patches of mycelium which may be readily peeled 
off from the smooth skin of the fruit. 
(d@) THE SUMMER SPORES, CONIDIA. 
A small portion of the mildew in its conidial stage is shown in Fig. - 
1. Only a few of the filaments making up the felt-like coating are 
represented. At intervals along these horizontal threads, branches 
are given off which rise vertically and soon begin a process of cross 
division, thus producing the conidial spores. Four of these aerial 
branches are shown (Fig. 1, a), one of which is still young, while the 
others are fully grown and spore-bearing. The spores (Fig. 1, 6) 
as they form by this simple method of division fall from the tips of 
the threads and new ones continue to be formed from below. There 
is therefore an indefinite succession of spores from the same filament, 
the number depending upon the surrounding circumstances. These 
spores are colorless, and when produced in large numbers give the 
infested surface of the host a white, powdery appearance, as previ- 
ously mentioned. They are borne exposed in the greatest possible 
degree, and may be readily scattered by the wind and in other ways. 
These spores quickly germinate when they fall upon a moist place on 
the surface of the host and produce new horizontal threads, which 
soon develop new vertical branches (conidiophores) with their spores. | 
(e) THE WINTER SPORES OR ASCOSPORES. 
The formation of the sexual or ascospores may begin soon after the 
conidial spores appear, but usually they follow late in the season, 
and in many species (?) are rot produced at all. With the goose- 
berry mildew they begin to form early in the life of the fungus, and. 
by June may be found of full size. The initial stage in this forma- 
tion is shown in Fig. 3, Plate XI. At a point where two of the hori- 
zontal filaments come near each other lateral branches are given 
off, one from each filament, One of these is slender and does not 
differ in appearance from the rest of the filament (Fig. 3,a). Theother 
outgrowth soon becomes swollen and sometimes nearly pear-shaped 
