ORDER HYPHOCHYTRIALES G9 



less than 0.1 mm. tall, and consist of an upright, stout and few-branched, 

 nonseptate hypha with a basal holdfast. Whether this is a true hypha or 

 a rhizomycelium is not known, since neither species has been found again 

 since their original description. 



In Zygochytrium the main stalk is forked, each branch terminating in 

 a spherical, operculate sporangium. The contents escape as a naked mass 

 which soon forms a thin membrane. In the interior the protoplasm divides 

 into many posteriorly uniflagellate zoospores which escape by the irregu- 

 lar rupture of the enclosing membrane, and soon germinate. Between the 

 main forks of the fungus short branches grow which meet and unite, 

 forming a zygospore in a manner very suggestive of zygospore formation 

 by the Mucorales. This thick-walled spore germinates soon by a slender 

 hypha and produces a new plant resembling the parent plant. This fungus 

 is yellow and grows on dead, submerged insects. (Fig. 21A-F.) 



In Tetrachytrium, which is blue-green in color, the nonseptate main 

 stalk bears three or four somewhat recurved branches on some of which 

 develop terminally spherical, operculate gametangia. Their contents 

 escape in the same manner as from the zoosporangia of Zygochytrium 

 and in a similar manner become invested in a thin membrane. Within 

 this are formed four posteriorly uniflagellate gametes which unite by 

 twos to form thin-walled, nonflagellate zygospores. After a little while 

 these germinate to form new plants. The gametes which do not unite do 

 not germinate. Occurring on dead plant material and even on dead 

 beetles in water. (Fig. 21G-M.) 



Until these fungi can be found again it will be impossible to decide 

 whether they really belong to the Chytridiales or to a group of fungi that 

 have a true mycelium. Their relationship may be with the operculate 

 Cladochytriaceae. 



Order Hyphochytriales. The organisms making up this order show a 

 close parallelism in body structure to the Chytridiales with which they 

 have been usually associated. They differ, however, in the type of zoospore 

 which is anteriorly uniflagellate. In Rhizidiomyces apophysatus Zopf, 

 Couch (1941) demonstrated that this single anterior flagellum is of the 

 tinsel type in contrast to the posterior flagellum of the Chytridiales which 

 is of the whiplash type. The cell walls may show positive cellulose reaction 

 in a few cases but in some species chloriodide of zinc calls forth no charac- 

 teristic cellulose coloring. Karling (1943) has grouped these forms with a 



Fig. 21. Chytridiales. (A-F) Zygochytrium aurantiacum Sor. (A) Mature plant. 

 (B) Emptied zoosporangium, showing operculum. (C) Extruded protoplasm has 

 formed zoospores. (D) Zoospores escaping. (E) Plant with beginning of conjugation. 

 (F) Mature zygospore. (G-M) Tetrachytrium triceps Sor. (G) Mature plant. (H) Proto- 

 plasm escaping from gametangium. (I) Four planogametes formed in the extruded 

 protoplasm. (J) Gametes escaping. (K) Gametes uniting. (L) Zygote beginning to 

 germinate. (M) Young plant. (After Sorokin: Botan. Ztg., 32(20) :305-315.) 



