5 



PHYCOMYCETEAE: LAGENIDIALES 

 AND SAPROLEGNIALES 



IN THE two foregoing chapters have been discussed organisms, chiefly 

 aquatic or soil inhabiting, with posteriorly uniflagellate swarm cells 

 and whose cell walls are deficient in cellulose or do not show the cellulose 

 reaction without preliminary treatment to remove some masking sub- 

 stances. Also organisms with a single anterior flagellum of the tinsel type 

 were discussed. In this and the next following chapter are treated forms, 

 many of them aquatic or soil inhabiting, in which the swarm cells are 

 anteriorly or laterally biflagellate and in which the cellulose reaction is 

 normally shown immediately upon application of chloriodide of zinc 

 without other preliminary treatment. The anterior flagellum is of the 

 tinsel type, the posterior one of the whiplash type. Here, too, a rather 

 well connected series can be followed from holocarpic, enddbiotic, mono- 

 centric forms up to fungi with extensive mycelium and complicated 

 modes of reproduction, both asexual and sexual. This series, of course, 

 may be read in the reverse direction, leading from the complex to simpli- 

 fied forms. The author does not follow Sparrow (1943) in considering that 

 the Plasmodiophoraceae are related to the other groups included in the 

 chapter since Plasmodiophora is apparently more closely related to the 

 Mycetozoa (see Chapter 2). 



Order Lagenidiales. The Hmits of this order are far from definite and 

 it may be that, as in the first edition of this textbook, the genera and 

 famihes here included should be placed in the order Saprolegniales. 

 Sparrow recognized the close affinity of some of these to that order by 

 placing the Ectrogellaceae and Thraustochytriaceae there. At present the 

 author is not convinced that enough is known of the structures and fife 

 histories of all of these rather simple or reduced forms to warrant their 

 distribution in separate orders. It therefore seems preferable to use the 

 order Lagenidiales as a temporary catchall for a number of genera which 

 perhaps are not too closely related, but which have in common the 

 characters given below. The members of this order are (except Thrausto- 



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