MICHIGAN ACADEMY OF SCIENCE. 
47 
Figure 1—Filament of mycelium showing conidiophore and a conidium mag¬ 
nified about 1,600. 
Figure 2—Conidiophores and conidia. . They quite frequently occur in clusters 
of three or four. 
Figure 3—Young conidia. 
Figure 4—Mycelium found on the surface of a midrib of a leaf; occasionally 
branching, but generally running parallel filaments lengthwise with the petiole; 
almost wholly on the surface. 
Photograph shows the general appearance of affected lettuce leaves. 
The name here proposed for the fungus is Didymaria perforans. It 
corresponds very closely to Engler and Prantl’s description of 
Didymaria. 
The main reasons why this fungus can not be a Marsonia are: 
1. The mycelium is superficial while the mycelium of Marsonia is 
sub-epidermal. 
2. There are no stromata, while, Marsonia, has typically well defined 
stromata. 
Other details indicate also that it is not a Marsonia; but the above 
two in themselves are sufficient to throw it out of that genus. In fact 
it would also throw it out of the group—the Melanconiales—which are 
separated from the ITyphomycetes chiefly by the presence or absence of 
a stroma. The Melanconiales have a well defined stroma while the 
Hyphomycetes have none. 
It is quite true that both these genera are but provisionally made 
in view of the fact that they belong to that group of supposed imperfect 
forms known as the Fungi Imperfecti; but so far as they are known, 
these provisional genera are of as much importance for the sake of 
convenience as any other genera. 
Agricultural College. 
