BLASTOCLADIALES 



The order Blastocladiales was founded in 1909 by H. E. Petersen 

 to accommodate a single genus, Blastocladia, which had been estab- 

 lished in 1878 by Reinsch and which up to 1909 had been included in 

 the Saprolegniales. It was apparent to Petersen, even from fragmentary 

 evidence, that the two fungi included in Blastocladia differed in several 

 important features from those comprising the Saprolegniales, for they 

 exhibited no cellulose whatsoever in the walls of the thallus and no 

 sexual reproduction, both well-marked characters of the Saprolegniales. 

 Furthermore, Thaxter (1896a) had already shown that the type of zoo- 

 spore produced by them was quite different in both its internal structure 

 and its method of attachment of the flagella from that found in the older 

 order, although this fact was not stressed by Petersen. In addition, 

 Thaxter's reinvestigation of Reinsch's species confirmed the presence 

 in B. pringsheimii Reinsch of highly peculiar thick-walled punctate 

 resting spores, which were apparently asexually formed. Blastocladia 

 remained a monotypic genus until 1896, when Thaxter, in connection 

 with his observations on Reinsch's species, described a second species, B. 

 ramosa. Scarcely two years after the establishment of Petersen's small 

 order Butler (191 1) added to it a second genus, Allomyces, which differed 

 in several striking features from Blastocladia. The distinctiveness of 

 Allomyces further justified the segregation of these fungi from the 

 Saprolegniales. Since then, other genera, Blastocladiella (Matthews, 

 1937), Catenaria Sorokin (Couch, 1945a), Coelomomyces Keilin (Couch, 

 1945b), Blastocladiopsis Sparrow (1950), and Catenomyces Hanson 

 (1944b) have been added to the Blastocladiales. 1 Monographs of the 

 order have been published by Kanouse (1927), Indoh (1940), and Spar- 

 row (1943). As it stands today the group is composed of clearly related 

 fungi. Furthermore, as a result of a series of discoveries concerning 



1 The names of two genera. Sphaerocladia (Stiiben 1939) and Clavochytridium 

 (Cox, 1939), which were included in this order in the first edition, are now regarded 

 as synonyms of Blastocladiella. 



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