THE ALG^-FUNGI (PHYCOMYCETES) 223 



215. Other phycomycetes. Of the forms that have here been 

 discussed, - — RMzojms, Saprolegnia, and Plasmopara, — each 

 represents an hnportant subdivision of the phycomycete class 

 of fungi. There are many molds closely related to MMzopus, 

 and some of them usually appear wherever there is decaying 

 organic matter. Several kinds of water molds are known, 

 and other parasitic forms which resemble Saprolegnia are the 

 cranberry-gall fungus (^Synchytrium Vacciniy, which attacks 

 the stem, leaves, flowers, and fruit of the cranberry plant ; 

 the "damping-off " fungus (Pythium DeBaryanurn), which, in 

 plant-house seed beds and sometimes in open fields, kills seed- 

 ling plants by attacking their cells at or near the soil, thus 

 causing them to wilt ; the brown rot of the lemon and other 

 citrous fruits {Pytliiacystis citrophthora), which is especially 

 injurious in California and is often a forerunner of the blue 

 mold (^Penidlliuni). Important plant parasites which in struc- 

 ture and habit resemble the grape mildew and potato blight 

 are the white or downy mildew ( GystopvM candidus, sometimes 

 called Albugo Candida) of plants of the mustard family (CVm- 

 ciferce'), as shepherd's-purse, the common radish, horse-radish, 

 cress, mustard, and turnip ; also another white mildew (Pero- 

 nospora parasitica) which infests many members of the mus- 

 tard family, including most of those mentioned for Cystopus, 

 as well as others ; downy mildew (Plasmopara cuhensis) of the 

 cucumber, pumpkin, and watermelon ; onion mildew (Peronos- 

 para Schleideni) ; downy mildew of lettuce (Bremia Laetucce) 

 and downy mildew of lima beans (PliytopMhora Pliaseoli). 



216. Summary of phycomycetes. In structure and methods 

 of reproduction this group resembles some of the green algse. 

 The frequently occurring coenocytic body suggests VaucJieria 

 and its relatives among the green algse. In reproduction 

 zoospores, zygospores, and oospores are formed, and the spe- 

 cialized sex organs, oogonium and antheridium, are present. 

 In some of the phycomycetes specialized asexual structures, 

 the conidia, are formed, and these germinate, usually producing 

 one or more zoospores. Evidently these conidia are sporangia 



