398 AQUATIC PHYCOMYCETES 



KEY TO THE SPECIES OF RHIZOSIPHON 



Prosporangium with a broad tubular vegetative system. . R. crassum, p. 398 

 Prosporangium without a vegetative system R. anabaenae. p. 400 



Rhizosiphon crassum Scherffel 



Arch. Protistenk., 54: 189, pi. 9, figs. 41-55. 1926 



(Figs. 11 K, p. 110; 24 D, p. 396) 



Prosporangium spherical or broadly fusiform when intercalary, 

 somewhat clavate when terminal, on a broad tubular vegetative system; 

 sporangium broadly and somewhat irregularly pyriform and 14-18 u, 

 in diameter or flasklike and 9-26 u, high by 6.5-12 \i in diameter, arising 

 laterally from an intercalary prosporangium or apically from a terminal 

 one, with a broad conical prominent discharge tube, wall thin, smooth, 

 colorless; zoospores spherical, 3 u. in diameter, with an inconspicuous 

 faintly refractive basal globule 1 jx in diameter or with several highly 

 refractive granules, with a posterior flagellum 18 u long, escaping 

 singly and amoeboidly through the open apex of the discharge tube 

 and remaining for a time near the orifice before darting away; resting 

 spore round-oblong, broadly fusiform and 10-12 by 15-25 jx, or nearly 

 spherical (ellipsoidal) and 6-12 by 8-15 jx, wall double-contoured, 

 smooth, colorless, contents with many colorless coarse highly refractive 

 globules, upon germination forming a narrowly pyriform sessile spo- 

 rangium with a smooth colorless thin wall. 



Parasitic on Filar szkya sp., Scherffel {loc.cit.), Hungary; Anabaena 

 spiroides var. crassa, Anabaena sp., A. ajfinis var. intermedia, coll. 

 Griffiths (1925), Canter (1951: 129, figs. 1-3, pi. 8, pi. 9a), Great 

 Britain; Anabaena spp., coll. Rohde, Canter (loc. cit.), Sweden. 



Rhizosiphon crassum has a remarkable effect on the coloration of the 

 filaments of Filarszkya. The infected cell and adjacent cells turn deep 

 wine-red (see under "Parasitism," p. 116). Such a color change has not 

 been noted in Anabaena (Canter, 1951: 135). An unusual feature of 

 this species' development is the production of a strongly vacuolate 

 foamy stage in the sporangium just prior to zoospore formation, a 

 condition reminiscent of the Saprolegniales. 



Scherffel considered that, in spite of the hypha-like nature of the 



