Dale —Observations on Gymnoascaceae. 585 
differs under different conditions. For example, oidia were 
sown in plates of beer-wort gelatine. The sowings were made 
from a pure culture, and yet two different kinds of colonies 
were formed — a dense kind and a loose kind. This difference 
was due simply to the fact that the dense colonies were sub- 
merged, while the loose form was growing on the surface of 
the medium. 
Microscopic examination of the oidium-bearing hyphae 
shows that they consist of erect hyphae branching dichoto- 
mously with great regularity (Figs. 55—57). When more 
highly magnified the protoplasm in these branches is seen 
to be collecting into regular squarish masses, each containing 
a large vacuole (Fig. 55 c). Finally, walls appear between 
the masses of protoplasm, and the walls break up into oidia 
(Fig. 56 a), which are at first flat at the ends, but which later 
become rounded (Fig. 57 ). Each oidium (Fig. 57 ) is larger 
than an ascus. The oidia readily germinate and form cultures 
indistinguishable from those grown from ascospores 1 . 
Amongst the vegetative hyphae of the oidium-bearing 
mycelium may often be seen thicker hyphae, which, however, 
bear branches of varying thickness (Fig. 58 ). Some of the 
thicker hyphae show the pyriform swellings (Fig. 59 ), the 
cyst-like ends to some hyphae, and the beaded appearance 
of other hyphae (Fig. 60), which are characteristic of the genus 
Gymnoascus and which have also been observed in other genera, 
e. g. in Onygena equina 2 . 
Besides the erect hyphae oidia may occur on the ascus- 
bearing mycelium, between the layer of sexual coils and the 
vegetative hyphae imbedded in the nutritive medium, but 
lying on the surface between the medium and the ascogenous 
layer. 
1 The mycelium of another species of Gymnoascus , still under culture, behaves in 
a similar manner. 
2 Marshall Ward, Onygena equina, Willd., a horn-destroying fungus, Phil. 
Trans., series B, 175, vol. cxci, pp. 269-291, PI. XXI, Figs. 11 and 12, PI. XXII, 
Fig. 13 (1899). 
