ORDER CHTTRIDIALES 



49 



I 



It is likely that all zoospores of these species are potentially either 

 gametes or zoospores, depending upon the environment and the oppor- 

 tunity for union of the cells. The earlier emerging zoospores usually do 

 not fuse but those emerging later, especially if from separate zoosporangia, 

 do. For most species of the genus, sexuality has not been demonstrated. 

 Treatment with chloriodide of zinc does not reveal any cellulose reaction 

 in those species of the genus that have been tested except in 0. radicale 

 Schwartz and Cook (1928). (Fig. 9.) 



The genus Pseudolpidiopsis was founded by Minden (1915) to include 

 an organism studied by Zopf (1884), parasitic 

 in algae of the family Zygnemataceae , which 

 was similar to Olpidium in asexual reproduc- 

 tion but different in sexual reproduction. He 

 named it Olpidiopsis schenkiana Zopf. Sexual 

 reproduction occurs within the host cell by 

 the union of two adjacent cells, the contents 

 of one passing into the other which forms a 

 thick wall to which the empty smooth cell 

 wall of the male cell adheres. Since this is the 

 type of sexual reproduction characteristic of 

 the genus Olpidiopsis in the Order Lageni- 

 diales doubt has been thrown on the accu- 

 racy of Zopf's description and figures (1884) 

 of the zoospore as posteriorly uniflagellate. 

 Sparrow (1942) and others are inclined to 

 unite the two genera and place them in the 

 Olpidiopsidaceae. Pleotrachelus, with many 

 exit tubes from the sporangium is otherwise 

 similar to Olpidium. Nothing is known as 

 to the sexual reproduction although resting 

 spores are produced in one of the three 

 definitely known species. These species occur 

 in molds of the genus Piloholus and in the fresh-water alga Oedogonium. 

 (Fig. 10.) 



Rozella includes eleven species recognized by Sparrow. They are all 

 parasitic in fungi of the Blastocladiales, Monoblepharidales, Sapro- 

 legniales, Peronosporales, Chytridiales, and a few other groups, mostly 

 in fresh water but one species in salt water. After entering the host cell 

 or filament, which frequently becomes considerably hypertrophied, the 

 organism remains naked for some time, finally producing a thin wall 

 which fuses with the host wall. In some species the organism becomes 

 septate into a series of several sporangia. The posteriorly uniflagellate 

 zoospores escape through one or more inoperculate exit papillae. Resting 



Fig. 10. Chytridiales, Fam- 

 ily Olpidiaceae. Pleotrachelus 

 fulgens Zopf. Zoosporangium 

 in Piloholus sp. (After Zopf. 

 Courtesy, Sparrow : Aquatic 

 Phycomycetes, Exclusive of 

 the Saprolegniaceae and Pyth- 

 ium, Ann Arbor, University 

 of Michigan Press.) 



