2 1 2 Barrett . — Development and Sexuality of some 
of his studies on the development of what he supposed to be Olpidiopsis 
Saprolegniae , (A. Br.) Cornu. Unable, after much searching, to find an 
adjacent cell associated with the resting spores, he concluded that so far as 
O. Saprolegniae was concerned it was not present, and he strongly suspected 
that it was absent in Cornu’s other species. Believing that Cornu was mis- 
taken concerning this point and the diagnosis "of his genus was incorrect, 
Fischer (12), in a later work, rejected the adjacent cell character and made 
the genus Olpidiopsis to include only those forms with resting spores which 
are not formed as the result of a sexual act. He accepts three of Cornu’s 
species and considers the other two doubtful. 
Schroter (22), in the ‘ Kryptogamenflora von Schlesien ’, accepted the 
change made by Fischer, and established the new genus Diplophysa for 
these parasites possessing an adjacent cell. 
In 1892, in Rabenhorst’s ‘ Kryptogamenflora ’, A. Fischer (13) gives 
an explanation of the cause of the confusion which his former work created. 
In the meantime he discovered a species on Saprolegnia which possessed 
a resting spore with an adjacent cell. This fact convinced him of the 
correctness of Cornu’s observations, and he therefore restored the genus 
Olpidiopsis for the form with the adjacent cell. 1 
Inasmuch as the life-history of these organisms, especially the sup- 
posed sexual stage, is still imperfectly known, through the suggestion of 
Professor G. F. Atkinson, to whom I am very grateful for his continued 
advice and kindly criticisms, I am led to take up a study of a few of 
these forms. 
3. Study of Living Material. 
A. Methods and Material. 
The results of observations presented in this paper are based upon 
studies made on three species of the genus Olpidiopsis , Cornu (emend. 
A. Fischer), collected in the vicinity of Ithaca. Two are parasitic on 
Saprolegnia , the third on Aphanomyces . One of the former, found on 
S.ferax , agrees in every way with the species described and illustrated 
by A. Fischer in Rabenhorst’s ‘ Kryptogamenflora ’ as O. Saprolegniae , 
Cornu, but which, for reasons to be stated later, I believe is not Cornu’s 
species, but a new one for which I propose the name O. vexans . The 
other two species, one found on an undetermined Saprolegnia , and the 
other on Aphanomyces laevis, are strikingly similar in morphological 
characters, but because of their biological difference they are believed to 
1 1. c. p. 34. 1. Pseudolpidium Saprolegniae mihi. Synon. : Olpidiopsis Saprolegniae , A. 
Fischer, Schroter. Olpidiopsis Saprolegniae , Cornu pro parte. 2. Olpidiopsis Saprolegniae , 
(Cornu) mihi. Synon. : Olpidiopsis Saprolegniae , Cornu pro parte. Diplophysa Saprolegniae, 
Schroter. Pleocystidium, Fisch. 
