110 BULLETIN OF THE BUSSEY INSTITUTION. 
whole plant, and only reaches the surface through the breathing pores, 
which are found principally on the lower surface of the leaf, and are 
entirely wanting in the berries. Furthermore, in the mycelium of the 
Peronospora, cross partitions are not common. ‘The conidia of the 
Uncinula are produced in the following manner, as represented in 
Fig. 2. Some of the branches of the mycelium rise up from the 
surface of the leaf, either obliquely or at right angles. Frequent con- 
strictions are formed and transverse walls are produced at the constric- 
tions, thus forming a number of cells, which are the conidial spores. 
The uppermost cell grows larger than the rest, and drops off. The 
next cell then enlarges, and drops off in the same way, and new cells 
are formed in the filament, so that a succession of conidial spores is 
formed, which ripen and drop off. The spores germinate at once by 
pushing out a germinating tube, generally at one end, not by produc- 
ing a number of zoéspores as is the case with Peronospora viticola. 
Late in the summer, the perithecia and asci of the fungus are formed, 
and they are ripe about the last of October. Fig. 1 represents 
the perithecia, as found in October. As seen by the naked eye, the 
perithecia look like small black bodies. They occur on both surfaces 
of the leaves, but are most easily distinguished on the smooth upper 
surface, inasmuch as the under surface of the leaves of most of our 
grapes is covered with hair, by which the perithecia are concealed. 
Fig. 1 shows a perithecium magnified about 550 diameters. The 
central mass is an opaque sac with a cellular wall, from which is 
given off a number of appendages which are rolled up at the end. The 
perithecium measures from .07 mm. to .12 mm. in diameter. The 
appendages are from fifteen to thirty-two in number, generally very 
numerous, and are from three to five times as long as the diameter of 
the perithecium itself. There are several cross partitions in the appen- 
dages, and they occasionally branch. At the base they are brownish 
yellow, but grow lighter colored at the tip, which is quite hyaline. In 
removing the perithecia from the leaf, the appendages are frequently 
broken off in the middle, so that it looks as though the fungus were a 
species of Hrysiphe proper rather than of Uncinula. Inside the peri- 
thecia are the asci or sacs, Fig. 3, attached at the base and containing 
the spores. The asci vary from four to eight in number, but the more 
frequent number is six. The spores also vary in number, the average 
being six. 
