of the Genus Doassansia , Cornu. 3 
I wish here to express my indebtedness to my instructor, 
Prof. W. G. Farlow of Harvard University, for access to the 
literature bearing on the subject, as well as for assistance at 
every point. 
Doassansia alismatis ( Nees ), Cornu. 
This is the species which Cornu studied in detail, and 
which must be considered as the type of the genus. The 
structure of the sorus of D. alismatis is very distinct, and, as 
a result of the study of it in connection with the other forms 
referred to Doassansia , it has become necessary to separate 
them into several groups. 
D. alismatis is found in the leaves of Alisma natans and A. 
Plantago in Europe, Asia, and America. Harkness (Proc. Cal. 
Acad., ser. 2, vol. ii) has mentioned it as occurring upon Echi- 
nodorus rostratus. Kellerman (Trans. Kans. Acad.,vol. ix and 
vol. x) and Galloway (Bull. Agr. Bot. Dept., viii) give Sagit- 
taria variabilis as a host. These references refer to other 
species than D. alismatis ; the last two to D. sagittariae , while 
the first is an undescribed species of Entyloma with a compact 
sorus, related to D. decipiens (cf. p. 42). 
The first indication of the presence of D. alismatis is the 
appearance of a small circular spot, of a pale yellowish green, 
on the upper surface of the leaf. This spot increases in size 
and soon becomes lead-coloured on account of the developing 
sori which begin to form at the centre, and extend toward the 
periphery of the spot. At this stage, the spot is about a centi- 
meter in diameter. As it grows larger, the edges become wavy 
and irregular, the interior becomes more yellow and brownish- 
yellow as the exhausted tissues of the leaf collapse, and finally 
the brown and dead centre crumbles away and leaves a hole in 
the leaf surrounded by a discoloured border, at the periphery 
of which the formation of new sori may still be proceeding. 
The sori are not confined exclusively to these spots, but often 
occur singly in other portions of the leaf remote from any spot. 
The leaf of Alisma Plantago shows in cross-section a single 
layer of palisade-parenchyma, the walls of whose cells touch 
