2 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



While the parasites reported as causing damping-off are probably 

 not as numerous as the host species which are subject to it, a con- 

 siderable number are known. Two quite different types of damping- 

 off parasites may be recognized. In the first type we have fungi, 

 such as Pythiwn debaryanum Hesse and Cortlcium vagum B. and C., 

 soil inhabiting and primarily saprophytic, which attack a great 

 variety of hosts, and are at least better known, if not more destruc- 

 tive, as damping-off organisms than as parasites on older plants. 

 They are specialized as to the type and age of tissues which they at- 

 tack rather than as to host. The second type includes fungi less 

 common as saprophytes and with a relatively limited, sometimes very 

 closely limited, host range. Phoma betae, the systemic parasite of 

 sugar beet (37), is an excellent example of the host-specialized para- 

 site, transmitted in the seed and capable of seriously injuring various 

 parts of the older plant at different stages of growth as well as at- 

 tacking seedlings. 



Most damping-off parasites are intermediate in habit between the 

 extremes of these two types. Of those which are somewhat host 

 specialized, the following may be mentioned : 



Ph&mapsis vcxans, the cause of foot-rot of eggplant, reported by Sherbakoff 



(128) as a frequent cause of damping-off of this host and believed to be 



carried on -seed. 

 Gibberella sauMnetii (Mont.) Sacc. (29) and the imperfect fungi which kill 



grain seedlings as well as cause diseases of the older plants (80; 126, 



p. 218). Species of Gloeosporium and Volutella named by Atkinson (2, 



p. 269; 52) as able to kill seedlings or cuttings of particular host plants. 

 Olomerella (Colletotrichum) gossypii, described by Atkinson (1) and Barre 



(4) as likely to cause damping-off of cotton (112). 

 Fusarium lini, the flax parasite, reported by Bolley (14) as destructive .to 



young seedlings. 

 Phoma lingam, the cause of black-leg of cabbage, at least under inoculation 



conditions able to kill quickly seedlings of cabbage and other crucifers 



(72). 

 Peronospora parasitica (Pers.) De Bary, a downy mildew attacking cabbage 



and various other crucifers, reported as killing thousands of very young 



cabbage plants in Florida seed beds (41). . 

 The entomophthoraceous Completoria complete, on fern prothallia (1; 87, 



p. 203). 

 Bacillus malvacearum, a parasite of the. leaves of cotton plants, which can 



also cause damping-off of its favorite host (113) and the bacteria from 



diseased cucumber plants with which Halsted (53) caused typical 



damping-off of cucumbers. 



Damping-off fungi with wider host ranges include Phytophthora 

 fagi, Aphanomyces levis (100), Rheosporangium ap~hanidei*matus 

 (38, 39), Botrytis cinerea, and certain Fusaria. The so-called prop- 

 agation fungus, " vermehrungspilz," a sterile damping-off mycelium 

 which Sorauer (133, p. 321) believed related to Sclerotinia and for 

 which Ruhland (115) has erected a new genus, considered by both 



