72 PHYCOMYCETEAE 



Flagellum posterior, discharge tubes rarely more than one. 



Olpidium 

 Flagellum posterior, discharge tubes usually numerous. Pleotrachelus 

 Zoosporangium completely filling the host cell, the cell walls of the fungus 

 and host in close contact. RozeUa 



Vegetative cell elongating and by septation forming a series of zoosporangia. 



Family Achlyogetonaceae 

 More than two zoosporangia formed in a series. 



Zoospores encysting at mouth of exit tube. Achlyogeton 



Zoospores swimming away from exit tube without encysting. 



Septolpidium 

 Only two zoosporangia formed, separated by an isthmus. 



Bicricmm 

 Vegetative cell dividing internally into numerous zoosporangia or serving as 

 a prosorus, the zoosporangia arising in a cell developing 

 from the prosorus. Family Synchytriaceae 



Parasitic in higher plants; vegetative cell rather large, becoming a sorus or 



prosorus or resting spore. Synchytrium 



Parasitic in algae; vegetative cell small, becoming a prosorus or a resting 

 spore. 

 Sorus of zoosporangia formed within the host cell. 



Sorus dividing into a few sporangia which show no signs of flagella, each 



producing a number of zoospores. Micromyces 



Sorus dividing into many zoosporangia which are set free, part within the 

 host cell, part through a papilla into the surrounding water. 

 Occasionally a zoosporangium bears a feebly active pos- 

 terior flagellum. Zoospores minute, 2-5. Endodesmidium 

 Sorus of zoosporangia formed outside the host cell at apex of a discharge 

 tube which pierces the host cell wall and produces only a 

 few nonmotile zoosporangia. Micromycopsis 



Eucarpic, i.e., endobiotic, epibiotic, or interbiotic, with rhizoids or haustoria. 



Monocentric. Including both operculate and inoperculate 

 genera. 

 Zoospore cyst enlarging into a zoosporangium or prosporangium. 



Family Rhizidiaceae 

 Zoospore cyst enlarging into a zoosporangium. 

 Exit papilla or tube inoperculate. 



Subsporangial swelling (apophysis) lacking. 



Interbiotic (i.e., not closely attached to host cell, which is entered 

 only by the tips of the rhizoidal branches). 

 Rhizoidal system arising from the main axis. Rhizidium 



Rhizoidal system with several branches from the body of the 

 sporangium. Rhizophhjdis 



Epibiotic (i.e., closely associated with the host cell which is pene- 

 trated by the rhizoidal system). Rhizophydium 

 Subsporangial swelling present (scarcely differentiated in Ohelidium). 

 Ej^ibiotic. i Phlyctochytrium 

 Interbiotic. 



Apex of zoosporangium with mucro; a cup- or funnel-like base. 



Obelidium 

 No pronounced mucro; no cup- or funnel-like base. 



Zoosporangium somewhat stellate. Asterophlyctis 



