I 



OEDEE LAGENIDIALES 95 



chytriaceae) endobiptic and holocarpic in that they Hve within their host 

 cells, mostly as parasites, and lack rhizoids, the whole fungus body 

 becoming one or several reproductive units. Asexual reproduction is 

 accomphshed by the transformation of the plant body into a zoospo- 

 rangium which empties its anteriorly or laterally bifiagellate zoospores 

 into the water surrounding the host cell through an inoperculate exit 

 tube or tubes in the manner of Olpidium or Achlyogeton in the Chytridiales. 

 The zoospores may escape singly and swim away independently or may 

 encyst at the mouth of the exit tube and later escape and swim away. 

 In some cases the zoospores are not distinguishable in the sporangium 

 within the host cell but emerge as a mass of protoplasm to form an 

 external vesicle (as in Pythium) and there become organized and break 

 through the plasma membrane of the vesicle and swim away. In almost 

 all cases the zoospores are of the secondary type, i.e., more or less kidney- 

 shaped with one of the two lateral flagella directed anteriorly and the 

 other posteriorly. 



Sexual reproduction where known is by the contact of whole plants 

 or of special segments and passage of the contents of one into the other, 

 which immediately becomes a zoosporangium or which may become a 

 thick- walled resting spore (oospore). In the latter case there is usually 

 no periplasm. The uniting organs (gametangia) may be approximately 

 equal and similar in appearance or the antherid may be much smaller 

 than the oogone and fertilization may be accomplished by a conjugation 

 tube. The thick-walled oospore has been observed in some cases to 

 germinate as a zoosporangium. 



In the order as here defined it is exceedingly uncertain whether we 

 have a series progressing from a simple monocarpic fungus to a short 

 hypha of several reproductive units on the way toward the evolution of a 

 well-developed hypha such as we find in the Saprolegniales or Peronospo- 

 rales or, what may be equally likely, the fungi of this order represent 

 different degrees of reduction from various genera of those orders. In 

 conformity with the procedure in the Chytridiales-Monoblepharidales 

 series and in the Hyphochytriales the organisms in the series with 

 bifiagellate zoospores (the Biflagellatae of Sparrow) are arranged with 

 those of simple structure first. 



Karhng (1942) recognizes five famihes in the group that he calls 

 "Simple Holocarpic Bifiagellate Phycomycetes." He does not wish to 

 convey the idea that these are necessarily a single phylogenetic series, 

 especially in view of the insufficient knowledge of the life histories of the 

 majority of the described species and of the uncertainty of their rela- 

 tionship, either as primitive or as reduced forms. If the latter, some of 

 them may represent reductions from Saprolegniaceae, Pythiaceae, or 

 Leptomitaceae that have a greater or less similarity because in reduction 



