46 THE LOWER FUNGI— PHYCOMYCETES 



cells. In all such cases, summer sporangia result from zoospores 

 and resting spores from zygotes. In other species, young thalli 

 copulate {e.g., Olpidiopsis spp. and Pseudolpidiopsis spp.) and 

 a pore connection is formed between them. One cell then 

 functions as the female and, after receiving the contents of the 

 male cell, enlarges and is transformed by the thickening of its 

 wall directly into the resting spore. The spore does not lie free 

 in the oogonium as in the Oomycetes. The emptied male cell 

 remains attached to the spore even at maturity and was termed 

 the companion cell by earlier mycologists who failed to appreciate 

 its real character. In some cases, several male cells conjugate 

 with a single female cell, and the resting spore bears consequently 

 several companion cells. In Zygorhizidium a conjugation tube 

 is put out by one individual and its contents are discharged 

 through the tube into the other which then develops into the 

 resting spore. In Polyphagus a similar tube is formed but the 

 resting spore develops in the tube. 



It is evident in the light of this great variation in the sexual 

 process that the order Chytridiales can not be incorporated in 

 the old superordinal group Oomycetes, as has been attempted 

 by Schroter (1892: 63). 



In the separation of the families of the order the treatment 

 here adopted is not identical with that of any standard text. 

 Except in the incorporation of the Plasmodiophoraceae, it agrees 

 in the main with that of von Minden (1911: 226), though his 

 recognition of the family Hyphochytriaceae is not followed. 

 His monograph of the order is the most recent general treatment. 

 We have not seen fit to follow Gaumann (1926: 15) in excluding 

 from the Phycomycetes those lower families of the present order 

 which do not form mycelium. His limitation of the term Archi- 

 mycetes to such forms will prove confusing to all students who 

 have applied it in the sense of Fischer to the Chytridiales and 

 Ancylistales. 



Below in the discussion of the Plasmodiophoraceae the reasons 

 for the incorporation of this family in the Chytridiales are given. 

 The point is stressed that the order as here recognized is clearly 

 a polyphyletic group. The inclusion of an additional border 

 line family is consequently the more easily justified. The results 

 of future investigation will doubtless enable the student of 

 phylogeny to arrange the members of the order in several natural 

 lines, but at present this does not seem possible. Consideration 



