66 THE FHYCOMYCETES 



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ova of liver fluke of sheep, on boiled fluke eggs and on 0.25/ 

 agar fortified with fluke-ova extract. Karling (1938) grew Cate- 

 naria sphaerocarpa on cooked root tips of corn and onion. In 

 pure culture on 3% plain agar Couch (1939) isolated Rhizidio- 

 myces apophysatiis, Rhizophidhim carpopbihmi, and R. midti- 

 porinn and cultivated them through several transfers. Cox 

 (1939), using the same technique as Couch, isolated Clavochy- 

 tridiw7i stomophihnn. Whiff en (1941) grew Neph'ochytridhnn 

 auranthnn on boiled leaves of corn and on filter paper. The fact 

 that these investigators have succeeded to a certain degree in cul- 

 tivatingr some of the chvtrids has contributed materially to under- 

 standing their activities and stimulatinor interest in them. 



Reproduction. In some species two types of sporangia are 

 developed: thin-walled, or temporary, sporangia and thick- 

 walled, or resting, sporangia. The latter type is capable of hiber- 

 nating and probably arises after fusion of gametes. The sporan- 

 giospores, except in the Woroninaceae, are uniflagellate. Cyto- 

 logical details are largely wanting and, among the few species 

 that have been examined, are quite contradictory. Nuclei have 

 been described as arising by amitosis, nuclear budding, and frag- 

 mentation. Cell-plate formation has been described as it occurs 

 during cell division (delimitation of spores). Others have con- 

 cluded that cell division arises either by progressive cleavage 

 of the sporangium or by fragmentation of the protoplast. Mei- 

 osis has been described in connection with only a single species. 

 Amoncr the cytological studies dealing with reproduction are 

 those of Curtis (1920) on Synchytrhim endobioticimi, Kusano 

 (1930) on Synchytrhim fidgens, Karling (1937) on Cladochy- 

 trhim replicatimi, and AIcLarty (1941) on Olpidiopsis achlyae. 



Olpidiaceae. The Olpidiaceae include approximately 50 spe- 

 cies, of which Olpidiimi brassicae, parasitic on the roots of vari- 

 ous seedlings, including cabbage and tobacco, is typical of the 

 family. Its uniciliate swarm spores settle upon the host, creep 

 over its surface in amoeboid fashion, come to rest, and produce 

 a thin wall. This wall is soon pierced by a narrow pore, the host 

 wall is also penetrated, and the spore content escapes. Then the 

 naked protoplast enlarges, and finally a wall is formed around 

 the mature thallus. At this point the entire thallus becomes a 

 sporangium; that is, it is holocarpic. During this process the 

 content of the thallus cleaves into a group of zoospores that 



