14 S etc hell. — -A n Examination of the Species 
of a light-brown colour. The spores are loosely packed 
together, nearly spherical., and io j u, to 15 M wide. The walls 
are thick and light-brown, and the contents bright and 
possessing one moderately large oil-globule. The cortical 
cells vary greatly in shape. On the free sides of the sorus, 
e. g. the upper and lower sides, they are brick-shaped (Fig. 74), 
reminding one very much of those of D. alismatis ; but where 
the sorus is crowded against another, they are more nearly 
cuboidal or nearly wanting (Fig. 73). 
The sori develope much as in D. alismatis , but the gelati- 
nization which precedes the ripening of the spores is more 
pronounced than in that species. 
The germination of this species has not yet been obtained. 
Sowings have been made in nine months of the year, but with 
no result. Different material from different localities and of 
different ages has been tried, but without success. Cultures 
in a decoction of horse-dung have been tried, both with fresh 
and with dried material, but the spores have obstinately 
refused to germinate. It is hoped that the germination may 
be obtained at some future time, and then the species can be 
compared more thoroughly with its neighbours. 
Although found on the same host as D. sagittariae , there 
are so many points of difference between them that they can- 
not be considered as the same. In the first place there is a 
difference in habit which is of some importance even in species 
with such feeble morphological characteristics as those of Do as- 
sansia. This difference in habit is constant. In the second 
place, the sori of D. opaca are two to three times the size of 
the sori of D. sagittariae . Thirdly, the spores are larger ; 
and finally, the cortical cells are different in the two species. 
Season. The pale-yellow spots that mark the first ap- 
pearance of the fungus begin to show themselves about the 
end of the month of July, and from that time on, until the frosts 
destroy the leaves of the Sagittaria , they continue to form. 
Distribution. At Newton, Mass., Far low ! and at Medford, 
Mass., and Norwich, Conn., Setchell ! In both of the last- 
