SAPROLEGNIALES 



169 



corresponds to Saprolegnin. The thread-like sporangium, con- 

 taining a single row of elongate zoospores, and the one-sporcd 

 oogonia constitute the chief points of difference (Figs. 62 and 63). 

 A parasitic tendency in the genus is pronounced. Several 

 species are facultative parasites, and A. phycophilus de Bary, 

 occurring in Spirogyra and Zygnema is apparently obligate in its 



Fig. 62.- — Aphanomyccs stellatus de Bary. (a) Portion of mature swarmspo- 

 rangium showing plasma portions forming swarmspores. (h) Plasma portions 

 escaping and collecting as spherical encysted spores at the apex of the sporan- 

 gium, (c) Spherical mass of spores at apex of emptied sporangium, (d) 

 Later stage; most of the spores gone leaving emptied cyst walls, (e) Mature 

 swarmspores. (/) Double swarmspores dividing, (g) Germination of spore 

 at close of second encystment to form mycelium. {After de Bary 1860.) 



parasitism. Many papers have appeared in recent years in 

 reference to the parasitic habit of A. euteiches Drechsler which 

 causes a root rot of various plants. This species has been 

 reported on peas (Haenseler, 1926: 467; Jones and Drechsler, 

 1925: 293), tomatoes (Drechsler, 1927: 287), and other hosts 

 (Linford, 1927: 133). Recently another speces, A. raphani Ken- 

 drick (1927: 19), has been reported as parasitic in roots of 



