100 



OOMYCETES. 



large, terminal, many-spored sporangium, many smaller, lateral sporangia are 

 formed with a few spores. Thamnidium. 



B. Asexual reproduction by sporangia and conidia. 



Order 4. Choanephoraceae. Choanephora with creeping endophytic my- 

 celium, and perpendicular sporangiophores. 



Order 5. Mortierellaceae. Mortierella polycephala produces on the same 

 mycelium conidia and sporangiophores. M. 

 rostafinskii has a long stalked sporangiophore, 

 which is surrounded at its base by a covering of 

 numerous felted hyphae. 



FIG. 83. PiZobolus. Mycelium (a, a), 

 with a sporangiophore (A) and the 

 fundament of another ( B). 



FIG. 81. Pilololus. Sporangium (a") with 

 stalk (a-c), which is covered by many 

 small drops of water pressed out by tur- 

 gescence. 



C. Asexual reproduction only by conidia. 



Order 6. Chsetocladiacese. The conidia are abstricted singly and aero- 

 genously. Chcetocladium is a parasite on the larger Mucoraceas. 



Order 7. Piptocephalidacese. The conidia are formed acrogenously and 

 in a series, by transverse divisions. The zygospore arises at the summit of the 

 conjugating hyphse, which are curved so as to resemble a pair of tongs. 'Pipto- 

 cephalis and Syncephalis live parasitically on the larger Mucorace. 



Sub-Class 2. Oomycetes. 



Sexual reproduction is oogamous with the formation of brown, 

 thick-walled oospores which germinate after a period of rest. 

 Asexual reproduction by conidia and swarmspores. Parasites, 

 seldom saprophytes. 



The oospores are large spores which are formed from the egg- 

 cell (oosphere) of the oogonium (oosporangium, Fig. 89, 95). A 

 branch of the mycelium attaches itself to the oogonium and forms 

 at its apex the so-called " antheridium " (pollinodium 1 ) : this sends 

 one or more slender prolongations (fertilising tubes) through the 

 wall of the oogonium to the egg-cell. 



1 Antheridium is preferred in this sub-class as keeping amore uniform term (Kn). 



