652 AQUATIC PHYCOMYCETES 



KEY TO THE GENERA OF THE CATENARIACEAE 



Thallus usually with strongly defined major axes along which in linear 

 series are reproductive structures alternating with sterile isthmuses ; 

 sporangia with one discharge tube Catenaria, p. 652 



Thallus much branched, diffuse; sporangia often with more than one 



discharge tube, endooperculate Catenomyces, p. 658 



CATENARIA Sorokin 



Ann. Sci. Nat. Bot., VI, 4: 67. 1876 

 (Fig. 44 A-G, p. 651) 



Thallus endobiotic, eucarpic, predominantly strongly polycentric, 

 branched or unbranched, septate, the septa delimiting the rudiments of 

 the sporangia, resting spores, or sterile isthmuses; sporangia generally 

 with a single discharge tube; zoospores posteriorly uniflagellate with 

 one or more globules, formed in the sporangium; resting spores thick- 

 walled, borne like the sporangia, upon germination functioning as a 

 sporangium, the planonts either giving rise directly to new asexual 

 plants or encysting at once, the cysts gametangia, each producing four 

 posteriorly uniflagellate isogamous gametes which fuse in pairs to form 

 bifiagellate zygotes, zygotes reestablishing the sporophyte thalli. 



Parasitic or saprophytic in the eggs of small or microscopic animals, 

 Anguillulae, liver flukes, mites, and adult rotifers, in Allomyces, and 

 so on; saprophytic in fresh-water algae and vegetable debris. 



Species of the genus develop highly specialized, often extensive, poly- 

 centric thalli. 



Much has become known in recent years about the morphology and 

 method of development in Catenaria anguillulae. Sorokin (1876) states 

 that the young thallus was septate and said that certain segments ex- 

 panded to produce the sporangia, while others remained narrow and 

 formed two-celled isthmuses. Dangeard ( 1 884— 85b), on the other hand, 

 did not believe that segmentation took place until after the appearance 

 of the branches and sporangial rudiments. He also detected the presence 

 of the rhizoids and observed the lack of constancy of the two-celled 

 character of the isthmus. J. B. Butler and Buckley (1927), E. J. Butler 

 (1928), Buckley and Clapham (1929), Karling (1934a; 1938b), and 

 Couch (1945a) have all verified the segmentation sequence described by 

 Dangeard. 



