232 AQUATIC PHYCOMYCETES 



Discharge pores variable in number and position, sessile or only 

 slightly elevated, rarely lacking 

 Sporangium predominantly spherical, subspherical, or angu- 

 lar" 

 Globule of zoospore small (less than half the diameter of 

 the spore body) 



Sporangium wall persistent after discharge of zoospores; 

 on various types of substrata 

 Typical sporangium large; zoospores numerous 

 On green algae 



Rhizoidal axis not inflated and haustorial; rhi- 

 zoids extensive 

 Resting-spore wall covered with minute spines; 



primarily on desmids R. globosum, p. 237 



Resting spore wall smooth or somewhat un- 

 dulate, bearing a small male cell; on 

 Spirogyra R. couchii, p. 241 



Rhizoidal axis somewhat inflated; rhizoids not 

 extensive 

 Sporangium spherical, with a single prominent 

 lateral discharge papilla; zoospores with- 

 out a prominent oil globule; on sporelings 

 of Oedogonium R. canterae, p. 242 



Sporangium spherical or slightly flattened, 

 with one to three sublateral, lateral, or 

 subapical discharge papillae; zoospores 

 with a prominent oil globule; on Ulothrix 



R. karlingii, p. 243 



On blue-green algae 



Rhizoids delicate; inconspicuous 



Sporangium with a single broad apical dis- 

 charge papilla, not angular; causing ring- 

 like contortion and excessive slime se- 

 cretion of the host trichomes R. deformans, p. 243 



Sporangium with two to four discharge papil- 

 lae which impart an angular shape; not 

 causing hypertrophy of the host 



R. subangulosum, p. 244 

 Rhizoids coarse, conspicuous. . R. megarrhizum, p. 246 

 On other Phycomycetes 



On reproductive organs of Pythium R. pythii, p. 247 

 On Choanephora R. mycetophagum, p. 247 



