Development and Sexuality of some Species of 
Olpidiopsis, (Cornu) Fischer . 1 
BY 
J. T. BARRETT, Ph.D. 
Associate in Botany , University of Illinois. 
With Plates XXIII-XXVL 
i. Introduction. 
O students of the lower Fungi, there is an especial interest attached to 
-L the genus Olpidiopsis , because it is one of the few genera of the 
Chytridiales that possess a supposed sexual stage. There is also an 
interesting relation, historically, between the genus and other closely 
related forms, which emphasizes the danger of hasty conclusions made on 
imperfect and insufficient observations. 
The genus Olpidiopsis was founded by Cornu (6), and although he did 
not diagnose the genus, it seems strongly probable that the main distinctive 
character was the presence in the life-history of its members of a resting 
spore to which was attached an empty smaller cell, called by him the 
‘ cellule adjacente \ This term was, of course, indefinite, and although 
Cornu believed there existed a sexual relation between the two cells, he had 
no definite evidence. 
Since the first recorded observation of a parasitic fungus on a member 
of the Saprolegniaceae by Nageli (18), the same or closely related species 
have occasionally been described by various observers. In certain cases, the 
resting spores, which are known to be so necessary for the correct determi- 
nation of the species, were not observed, hence we have no assurance what 
the forms were. However, the literature concerning these forms previous 
and subsequent to the founding of the genus Olpidiopsis is so related in one 
way or another, that it seems advisable to give a brief review of it here. 
As stated above, the first reference to one of these organisms parasitic 
on the Saprolegniaceae was made by Nageli in 1846. He observed in the 
swollen hyphae of what he called Achlya prolifer a , now supposed to have 
been Saprolegnia ferax , elongated oval structures which eventually dis- 
charged their contents, as small motile bodies, to the exterior through 
1 Contribution from Department of Botany, Cornell University, 142. 
[Annals of Botany, Vol. XXVI. No. Cl. January, 1912.] 
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