ORDER BLASTOCLADIALES 79 



and thorough washing the wall in Monohlepharis, according to von Wett- 

 stein (1921) and to Harder (1937), shows a violet coloration with chlor- 

 iodide of zinc. The author obtained the same reaction with an unidentified 

 species of Blastocladia. Harder claims that in AUomyces and certain other 

 members of the family the cell wall consists fundamentally of chitin. 

 Nabel (1939) makes the same claim for AUomyces, Blastocladia, and 

 Blastocladiella. In Coelomomyces a cell wall has not been demonstrated 

 on the vegetative mycelium. 



Order Blastocladiales. In the first edition of this textbook Blasto- 

 cladiales and the following order, Monoblepharidales, were included under 

 the latter name. Because of the slight differences in the structure of the 

 zoospores and of the type of sexual reproduction, where it is known, and 

 the production of resting sporangia the author now follows Sparrow (1943) 

 in recognizing two orders. In the Blastocladiales the posteriorly uni- 

 flagellate swarm cells (zoospores or gametes) usually possess a well- 

 marked "nuclear cap" attached mostly to the anterior surface of the 

 nucleus. In the Monoblepharidales the nuclear cap is not noticeable but 

 in the swimming cells numerous small granules are gathered at the apex 

 sometimes forming a sort of papilla. 



In the Blastocladiales sexual reproduction, where known, is by the 

 union of two equal or unequal motile gametes to form a biflagellate zygote 

 which germinates without becoming a resting spore. In the Mono- 

 blepharidales the egg is nonflagellate and after fertilization forms a thick 

 wall to become a resting spore. In the Blastocladiales, in addition to the 

 thin-walled zoosporangia, there are found also thick-walled resting spo- 

 rangia which, in Blastocladiella and AUomyces, have a close connection 

 with the alternation of sporophytic and gametophytic generations — an 

 alternation that is unknown in the Monoblepharidales. These resting 

 sporangia are spherical, ovoid, or pyriform, with a thick outer wall often 

 perforated by numerous pits, and a thin inner wall. On germination the 

 outer wall cracks open and the expanding inner wall produces one or more 

 exit papillae from which the swarm spores emerge. These latter are called 

 "planonts" by Sparrow (1943). 



Three families are tentatively recognized, Catenariaceae (Couch 

 1945a), Coelomomycetaceae (Couch, 1945b) and Blastocladiaceae. They 

 are distinguished as follows: 



Family Catenariaceae. This family is parasitic in worms or fungi, 

 or saprophytic in various other plant or animal substrata. The plant body 

 at first is tubular, mostly unbranched, coenocytic, swelling at more or less 

 regular intervals to form reproductive organs which are connected by 

 short, narrow isthmuses, septate at each end and sometimes in the 

 middle. These reproductive bodies are either thin-walled zoosporangia 

 discharging by exit tubes or, on more exhausted media, thick-walled 



