KEY TO THE ORDERS OF BIFLAGELLATE FUNGI 43 



nonflagellate cells and sexual reproduction is by the union of two gametes 

 or two gametangia. The Keys given below will serve to distinguish the 

 orders of this class. 



Key to the Orders of Posteriorly Uniflagellate Fungi 



Without true mycelium, at most a rhizomycelium. Alternation of sporophytic 

 and gametophytic generations wanting. Zoospores mostly without large 

 nuclear cap or "side body." Order Chytridiales (Chap. 3) 



Rarely without mycelium, mostly with multinucleate, coenocytic mycelium. 

 Sexual reproduction, where known, by the union of isoplanogametes or 

 anisoplanogametes. Alternation of sporophytic and gametophytic genera- 

 tions often present. Zoospores with large nuclear cap and "side body." 



Order Blastocladiales (Chap. 4) 



With multinucleate, coenocytic mycelium. Sexual reproduction by the union of 

 motile sperm with non-motile egg, to form thick-walled oospore. Alternation 

 of sporophytic and gametophytic generations wanting. Zoospores with 

 numerous small granules at the apex. Order Monoblepharidales (Chap. 4) 



Key to the Order of Anteriorly Uniflagellate Fungi 

 Only one order recognized. Order Hyphochytriales (Chap. 3) 



Key to the Orders of Anteriorly or Laterally Bifiagellate Fungi 



Holocarpic fungi, parasitic within animal or plant hosts (rarely saprophytic), 

 the whole organism being converted into a single reproductive organ (game- 

 tangium or zoosporangium) or a series of such organs, separated by septa. 

 Zoospores of primary type or much oftener of secondary type, preformed in 

 the zoosporangium or becoming organized in a vesicle formed at the apex 

 of the exit papilla or tube. Sexual reproduction by the union, sometimes 

 through a short conjugation tube, of two gametangia of equal size or more 

 often of an antherid and oogone. Oospore usually not surrounded by peri- 

 plasm. Order Lagenidiales (Chap. 5) 



Eucarpic fungi usually (but not always) with well-developed branched and 

 tapering holdfast system. The external fungus body [a system of usually 

 stout cylindrical, branched coenocytic hyphae, nearly uniform in thickness 

 or with large basal segments and slender branches. Reproductive organs 

 borne on the branches and making up only a small part of the whole fungus. 

 Asexual reproduction by bifiagellate zoospores, often dimorphic, rarely of 

 primary type only, often only of secondary type. Oogones with one or more 

 eggs, with or without periplasm. Fertilization by antherids to form thick- 

 walled oospores. Mostly saprophytic in soil and fresh water, in some cases 

 parasitic in roots, algae, fungi, or fresh-water animals. 



Order Saprolegniales (Chap. 5) 



Eucarpic fungi consisting of slender, cylindrical hyphae with or without haus- 

 toria, mostly growing within the tissues of living hosts (mostly plants), or in 

 dead organic matter in soil or water. Zoospores of secondary type only, 

 produced under water in slender or rounded zoosporangia and organized in 

 a vesicle at the mouth of the exit tube, or the zoosporangia (coiiidia) are 

 borne aerially and distributed by air currents, the formation of the zoospores 

 occurring in these conidia after they fall into water. In some genera zoospore 

 formation is omitted and the conidia germinate by germ tubes. Sexual 



