PHYLOOENY 



Kl.-i 



that the four genera and approximately nine species 

 which comprise this family ••ire too poorly known to 

 warrant definite conclusions for the present. As has 

 been pointed oui earlier, the- type genus Ectrogella 

 was formerly included in the chytrid family. Olpidia- 

 ceae, by Fischer ('92), Schroeter ('97), Petersen 

 (*05), Minden ('1 1 ). Gwynne-Vaughan and Barnes 

 ('26, '87), Fitspatrick ('80), and others, although 

 Zopf ( '8 t) emphasised its similarities to the Lageni- 

 diaceae (Ancy lis teen). Scherffel's ('25) discovery 

 that the zoospores are bifiagellate and diplanetic 

 necessitated the removal of this genus from the chy- 

 trids. and he accordingly made it the basis of a new 

 family. 



The shape and size of the thallus offer no definite 



suggestions about to the origin of the Bctrogellaceae 



because it may he oval, spherical, ellipsoid, or elon- 

 gate, as in many of the other families. Nevertheless. 



the grayish granular appearance of the protoplasm. 



the presence in mature sporangia of a large central 

 vacuole surrounded by a parietal layer of proto- 

 plasm, the method of cleavage or zoospore delimit.! 

 tion (ball inifi ). and the subsequent occurrence of the 

 homogeneous stage following cleavage indicate di- 

 rect relationship with the Saprolegniaceae, accord- 

 ing to Schcrffel. While such characters alone are not 

 always indicative of close affinity, they are supported 

 in this case by the diplanetic behavior of the zoo- 

 spores. As Schcrffel has shown in Ectrogella, the 

 primary swanners are usually apically bifiagellate 

 and isocont and swim directly away for a brief 

 period before encysting as in Saprolegnia, or they 

 may be atlagcllate. glide out. and encyst in a cluster 

 at the mouth of the exit tube as in Achlya. The sec- 

 ondary swanners in Ectrogella are lemon-shaped 

 and pvriform. usually with a ventral groove, later- 

 ally bifiagellate and heterocont with the shorter and 

 more active flagelbun extending forward in swim- 

 ming. In the genus Eurychasma the primary swarm- 

 era may encyst around the inner periphery of the 

 sporangium as in Dicti/itchtis, but the secondary 

 zoospores do not emerge through individual pores 

 in the sporangium wall as in the latter genus. In- 

 stead, they emerge from the cysts into the central 

 portion of the sporangium and then swim out 

 through the exit tube. In Eurychasmidium and 

 Aphanomycopsis the primary zoospores are reported 

 to behave like those of Achlya and Aphanomyces. 

 Secondary zoospores, however, have not been ob- 

 served in Eurychasmidium. 



Thus, in the family Bctrogellaceae the zoospores 

 may exhibit striking similarities in behavior and 

 structure to those of Saprolegnia, Achlya, Aphano- 

 myces and Dictyuchut. Furthermore, in Ectrogella, 

 Aphanomycopsis, and Eurychasma may be found 

 the same degree of reduction of the primary swarm- 

 ing period as occurs from Saprolegnia through 



Achlya and Aphanomyces to Dictyuchus. Whether, 

 on these grounds, the members of the Bctrogellaceae 



an- to be considered primitive- or reduced and degen- 

 erate aaprolegniaceoua species is not clearly evident. 

 Mycologists who adhere to the reduction hypothesis 



MONOItt'HAtlOlACIAl 



IIAUOCIAOIACIAE 



RHIZIOIACtAI 



StNCMTTIIACIAE 



OlUDIACtAl 



INIOMO'HTKORAtU 



lAflOIIGNIACIAt 



IIPtOMITACIAI 



rl«ONO.PU«ALlAt 



ClADOCNVUIACIAt 



HT*HOCkTTRIAC(AE 



'AIIEKiNACIAt 



'YTHIACIAI 



lAGfNIDIACIAI 



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»o.'.'-o> riogrllum 



HCIEROCONT UNICEIIULA* AIOAE 



Diagram 2. Phytogeny of the Phycomycetes based upon 

 the theory of their origin from unicellular algae. After 

 Bessey 19i2. 



may well argue that the thallus of this family has 

 undergone reduction while the zoospores have re- 

 tained their diplanetic behavior. Schcrffel. however, 

 regarded them as primitive and held that the type of 

 diplanetism exhibited is derived from the Proteo 

 myxa or Monadineae instead of the Saprolegniales. 

 In line with his belief that the Phycomycetes in gen- 

 eral are derived from the Monadineae as shown in 

 diagram 1, he accordingly concluded that Ectrogella 

 and Aphanomycopsis may have originated from bi- 

 fiagellate heterocont genera similar to Aphelidiop 

 sis. Pseudosporopsis, and Amylophagus and possi 

 hi v inherited their diplanetic habit from an ancestor 

 like Pseudospora leptoderma. He also believed that 

 the large central sap cavity or vacuole present in 

 zoosporangia is a relic of a proteomyxean ancestor. 

 On the basis of the type of sexual reproduction 

 Schcrffel further believed that Ectrogella may be 



connected on one hand with the Saprolegniaceae anil 



Leptomitaceae through Aphanomycopsis and on the 

 other hand with the Peronosporaceae through Olpi- 

 diopsis, the Lagenidiaceae, and Pythiogeton. How 

 ever, as has been emphasized before, the occurrence 

 of sexual reproduction in the Bctrogellaceae lias 

 not been conclusively proven. Resting spores are 



known in only three species. In E. per farcins they 

 appear to be nothing more than vegetative thalli 



which have encysted and developed thick walls. 



Scherffel regarded the resting spore of /•.'. Licmn- 



phorae as an oospore in a rudimentary oogonium. 



although he did not actually observe sexual fusion. 

 As the- present author has already peiinteel out. this 



resting spe,r>- may pe.ssibly be- nothing more than the 



