TO 
JotjItXAL Of TfiE ROYAL HGRircTjLTOHAL SOCIETY. 
manner Some of the branches of the mycelium rise up from the 
surface of the leaf, either obliquely or at right angles. Fre¬ 
quent constrictions are formed, and transverse walls are produced 
at the constrictions, 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 producing a number of zoospores as 
in Peronospora. 
“ Late in the autumn the perithecia and asci of the Fungus are 
formed, and they are ripe about the last of 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 distin¬ 
guished 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. 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 to T2 millimetres in diameter. The appen¬ 
dages 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 appendages, and they occasionally branch. At 
the base they are brownish-yellow, but grow lighter-coloured at 
the top, 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 Erysiphe 
proper, rather than an TJncinula. Inside the perithecia are the 
asci or sacs 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. 
“ In short, the TJncinula spiralis appears in two phases : first, in 
the form of a white flocculent mould on the leaves, stalks, and 
grapes in midsummer ; and secondly, in the form of perithecia, 
with rolled appendages, later in the season. Compared with 
Peronospora viticola , it is more superficial, growing over the 
epidermis ; but, on the other hand, is practically more dangerous, 
as it attacks the fruit, which is not the case with the Peronospora. 
