THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



dia of Saprolegnia. However, an intensive study by 

 Cornu in 1872 settled forever the question of 

 whether they are parasites or relate to the life cycle 

 of the host. He proved conclusively their parasitic 

 nature and established the genera Olpidiopsis and 

 Woronina for the biflagellate species which occur in 

 Achhia, Aphanomyces, and Saprolegnia. Like Braun 

 he included these parasites in the Chytridiales. 

 Cornu observed that the resting spores were usually 

 accompanied by one or more attached, thin-walled, 

 empty vesicles which he assumed to be male cells or 

 antheridia. In 1878 Reinsch observed the passage 

 of the protoplasm of the small cell into the larger 

 one, and since that time the resting spores have 

 been generally regarded as zygotic in origin. Cornu 

 and Reinsch observations were followed by the early 

 studies of Fischer which contributed much to our 

 knowledge of the developmental phases of these 

 fungi. His observations and conclusions were never- 

 theless incorrect and confusing in several respects, 

 and it was not until 1892 that he corrected some of 

 his errors. Subsequent students of these olpidioid 

 parasites, including Zopf ('84.), Schroeter ('86, '97), 

 Petersen ('09, '10), Minden ('11), and others, con- 

 tinued to include them in the Myxochytridiales, al- 

 though Lotsy ('07) and Vuillemin ('08) emphasized 

 that the so-called chytrids with biflagellate zoo- 

 spores have a different origin from those with uni- 

 flagellate zoospores and should be sharply separated 

 from the latter. These differences were clearly rec- 

 ognized by Scherffel in 1925, who for the first time 

 removed Olpidiopsis and similar genera from the 

 Chytridiales and placed them at the bottom of a 

 Saprolegniales-Peronosporales series. Seherffel's in- 

 terpretation has been followed by a few mycologists, 

 particularly Weston ('35, '41) and Sparrow ('35, 

 '42). 



In the meantime, while data about the simple 

 olpidioid parasites were accumulating, extensive 

 studies had been made on the more complex, elon- 

 gate and mycelioid species at the other end of the 

 series. In the group now known as the Lagenidiaceae 

 the genera Mysocytium and Lagenidium were dis- 

 covered and created by Schenk in 1858 and 1859. 

 Because of their elongate thalli and the fact that the 

 zoospores may be formed in a thin, extramatrical 

 vesicle, these species were first regarded as members 

 of the genus Pythium by Schenk, Pringsheim ('58, 

 '60), and Walz ('70), although it was not then 

 known that the zoospores are biflagellate. These 

 workers figured and described the zoospores as uni- 

 flagellate, but the subsequent studies of Zopf ('78, 

 '79, '84, '87) proved the presence of two flagella as 

 well as the fact that sexual reproduction in many of 

 the species is heterogamous. These discoveries 

 coupled with the association of Mysocytium and 

 Lagenidium species with Pythium in mycological 

 literature emphasized their relationship to the 

 higher filamentous Oomycetes, and the Lagenidia- 

 ceae were accordingly never included directly in the 

 Chytridiales. Most mycologists have subsequently 



incorporated this family with the Saprolegniales. 

 Since the time of Zopf several unicellular, olpidioid 

 species of Myzocytium and Lagenidium have been 

 discovered, the thalli of which are strikingly similar 

 to those of Olpidiopsis, so that the gap between the 

 Olpidiopsidaceae and the elongate mycelioid mem- 

 bers of the Lagenidiaceae has been bridged as far 

 as thallus structure is concerned. 



These simple Phycomycetes are fairly common in 

 nature and almost world wide in distribution. So far 

 they have been reported from Europe, Asia, and 

 North America, and when more extensive studies 

 are made they will doubtless be found to occur in 

 Africa and Australia also. They are ubiquitous in 

 host range and occur in diatoms, blue green, green, 

 brown, and red algae, fungi, liverworts, mosses, 

 gvmnosperms. and angiosperms. Among animal 

 hosts they have been reported in infusoria, rotifers, 

 nematodes, weevils, mosquitoes, copepods and 

 crustaceans. They are predominantly aquatic and 

 may occur in marine as well as fresh water. Most 

 species of the families Ectrogellaceae and Sirolpi- 

 diaceae parasitize marine algae. The majority of 

 species are parasitic and eventually kill their hosts, 

 while others are weakly parasitic or saprophytic. 

 Obligate parasitism has been reported for a few spe- 

 cies. They may cause marked reactions in their hosts 

 which involve increased cell division and enlarge- 

 ment and lead to gall formation. Other species 

 merely kill and absorb most of the contents of the 

 host cells. Only one species appears to be of eco- 

 nomic significance. Lagena radicicola in conjunction 

 with other fungi causes a root disease of wheat, 

 barley, rye, and corn which is characterized by 

 stunted curved roots and a reduction in the root 

 system as a whole. The stems of infected plants are 

 considerably shorter than those of normal indi- 

 viduals, while the leaves may become pale-green 

 and lighter in color and under certain conditions 

 show "browning symptoms." 



Since several of these species do not appear to be 

 closely related, differences in types of development 

 are to be expected, and it is impossible to give an 

 introductory account which will apply to all fami- 

 lies and genera. In the family Woroninaceae, as it 

 is here interpreted, the vegetative assimilative thal- 

 lus has been described as a plasmodium which un- 

 dergoes cleavage at maturity. The segments thus 

 formed may develop either into zoosporangia or 

 resting spores. The former may be united in a spo- 

 rangiosorus or lie free, and give rise to zoospores 

 which are discharged to the outside and reinfect the 

 host. The resting spores whenever formed usually 

 appear as the fungus culture becomes older and 

 more mature. In W. polycystis they are usually ag- 

 gregated in compact cystosori as in some genera of 

 the Plasmodiophorales, while in other species they 

 lie loose and free. Like the sporangia, they form 

 zoospores in germination. Neither zoosporangia nor 

 resting spores have been observed in Pyrrhosorus. 

 The spore mother cells which comprise the sorus 

 divide three times to form eight free, thin-walled 



