BULLETIN OF THE BUSSEY INSTITUTION, 111 
In short, the Uncinula 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. 
The European grape mould resembles very closely Fig. 2. Our 
figure, which was of necessity drawn from a dried specimen, represents 
the cells as somewhat blunt and squarish. When fresh, they were 
more rotund and slightly constricted at the joints, resembling even 
more closely the figures of Mohl* and Fresenius f than at present. 
If there is any difference between the European Oidium Tuckeri and 
the conidial form of our own Uncinula spiralis, it lies in the somewhat 
smaller size of the latter, but that could hardly be called a specific 
_ difference, since Mohl has called attention t to the fact that the spores 
of Oidium Tuckeri itself are variable in size. The European grape 
mould was first named by Berkeley Oidium Tuckeri after the discoverer 
of the fungus; but, later, recognizing that the fungus was evidently 
closely related to the conidial forms of the species of Hrysiphe, he 
renamed it Hrysiphe Tuckerit. The perfect ascophorous form of 
Oidium Tuckeri is not definitely known, although some writers have 
associated it with other forms. Fuckel,§ for instance, considers that it 
is a conidial form of Spherotheca Custagnei, a common mildew in this 
country and Europe, growing on the leaves of many different plants, 
especially on hops. His view, however, is not generally accepted. 
In answer, then, to the question whether we have O/dium Tuckeri 
in this country, it should be said that we have a common fungus, Un- 
einula spiralis, whose conidial form is practically undistinguishable 
from Oidium Tuckert. Whether or not it is precisely the same thing 
can never be known until European botanists have found out to what 
perithecial form their own grape mildew belongs; for it is a fact that 
some of the species of the Perisporiacee, to which order Oidium Tuckeri 
undoubtedly belongs, cannot be distinguished from one another by their 
* “ Bot. Zeit.,” 1853. Plate XI., Fig. 7. 
+ “Beitr. zur Mykologie,” Plate IX., Figs. 14 and 15. 
t “Bot. Zeit.” 1853. 
§ “Symb. Mycolog.” 
