66 THE SAPROLBGfNIACE^ OF THE UNITED STATES, 



grains ; in short, a large part of the minuter organisms of fresh waters, to which they 

 are chiefly restricted. A few species, however, are marine. 



The Ancylistacece inchide a few species, chiefly parasitic upon Conjugate and 

 Anguillulce. The young plant is mycelium-like, but is entirely consumed in the 

 formation of the reproductive organs. These are sporangia, oogonia, and antheridia. 

 From the union of the protoplasm of the last two, there results in each case a single 

 oospore. While clearly related in their vegetative structure and habits with 

 the Chytridiacece, these plants may be regarded as forming, in their reproductive 

 organs, a transition to the higher Oomycetes. 



The Saprolegniacece are to be discussed later. 



Closely related to them, but differing in essential particulars, is the single genus 

 MonoMepIiaris which forms the type of a distinct family. It has been studied only 

 by Cornu, who has described three species. According to this author, the plants 

 have sporangia with uniciliate zoospores ; and the oospheres, formed singly in the 

 oogonia, are fertilized by motile uniciliate antherozoids, produced in a cell cut off just 

 below the oogonium from its supporting filament, which gains access to the oosphere 

 through an opening at the apex of the oogonium. These plants are saprophytes. 



The PeronosporacecE are represented among aquatic fungi by some of the mem- 

 bers of a single genus, Pythium. Like the rest of the family, the members of this 

 genus have an abundant mycelium from which are developed the sexual organs, 

 antheridia and oogonia. Each of the latter produces a single oosphere from a portion 

 of its protoplasm, the rest remaining as "periplasm," and ultimately forming an outer 

 coat about the spore. There appears to be an actual passage of protoplasmic 

 substance from theantheridiura to the oosphere, constituting a real act of fertilization. 

 In Pythium, as in some of the Ancylistacece, the zoospores are formed outside of the 

 mouth of the sporangium from the contents of the latter, after it has been extruded 

 in a single mass. The aquatic species of the genus are parasitic on water plants or 

 saprophytic on organic remains. One or more species attack terrestrial Phanero- 

 gams. 



The American literature of these various groups is confined to a few scattered 

 notes in addition to that quoted in the present paper, with the exception of Prof. 

 Farlow's account of the genus Sy/icJiytrium of the Chytridiacece. Its members are, 

 however, not aquatic. 



This brief preliminary account may suffice to indicate the neai" relationship of all 

 the aquatic fungi and to suggest the great morphological interest which attaches to 

 them ; while it may suitably preface the detailed discussion of the family which 

 forms the subject of the present contribution. 



