56 



33. Cystopus candidus Lev., Syll. VII ''\ Fisch. IV\ Syn: Uredo 

 Candida Pers., Schum. no 1576, Hvid Brandstev (H. 37 ^^'), Korsblom- 

 sternes Hvidrust (R 71 ^^ 04 a ™ c. icon. 6. 02 a ^^), Lit: R 93 c ^^ c. icon., 

 Lind 10 k. 



Very common, but to a different degree on the different host-plants ; 

 even within the Umits of the same species of host-plants a difference 

 as to the susceptability may be found; I have, for inst., seen fields of 

 Roripa armoracia consisting of a mixture of two varieties ; one variety 

 was always affected the other not at all. Rostrup was of the same 

 opinion (88 a '"') as de Bary that the plants could only be infected 

 on quite a young stadium, this has later on been confirmed from an 

 other side (Eberhardt 04). A. Hansen (88) has noticed that one lot of 

 cabbage-plants in their second year was quite destroyed by Cystopus 

 while a second lot was not infected at all; the same case has been 

 observed by me near Stege where this fungus completely prevented 

 cultivation of Brassica oleracea for seeds; the owner told me that the 

 groups of white conidia broke forth, simultaneously on all plants every 

 year in the beginning of August. 



Melhus has recently (11) experimented with this species. He states 

 that the leaves of the host are as susceptible to conidia of Cystopus 

 as the cotyledons are. And also that there may exist more biological 

 species of Cystopus candidus on the crucifers. It was not possible to 

 infect more than 50 % of the cotyledons or leaves of Sinapis alba 

 with conidia from Raphanus. And less than 1 per cent of the Bras- 

 sica-plants inoculated became infected. 



Closer observations of the biology of this fungus are badly wanted. 



It may be found from May to October. The oldest specimen of the 

 collection of Rostrup is from June 1861. It is curious that neither Ro- 

 strup nor anyoneelse has been able to find it in this country on 

 Thlaspi airvense. 



Draba incana. J. Legstar! (Exc. ^^/y 1910). Cochlearia officinalis. J. LegstBr!. 

 Berteroa incana. F. Espe! Klingstrup. Roripa armoracia. (R 93 k ■"") common. 

 Camelina linicola. F. Ringe!. Capsella bursa pastoris common. Teesdalia nudi- 

 caulis. J. Bustrup!, Bruunshaab!, Feldborg; F. Skaarupor; Thorseng, Breg- 

 ninge; Falst. Beta. Lepidium campestre. S. Aamose, 0gaard!. Lepidium perfo- 

 liatum. Am. Klavermarken. Coronopus Ruelii. Am. Fslled; L. Nysted Gader; 

 B. Svaneke (R 06 dd ^''^). Cardamine pratensis. Am. (O. R.). Conringia orientalis. 

 J. Dvergetvedl S. Landbohejskolens Have. Turritis glabra. F. Ringe!, Vejstrup 

 Aaskov, Skaarup. Arabis arenosa. J. Vilsted by Legstar!. Arabis alpina. S. 

 Sallerod ! Botanisk Have (E. W.). Stenophragma thalianum. F. Ringe ! Kling- 

 strup; S. Roskilde (C. Thomsen). Alliaria officinalis. J. Skive!. Barbarea lyrata. 

 F. Dalum (Jak. Lge), Ringe!. Sisymbrium officinale. J. Silkeborg; F. Svendborg; 

 S. Stavnsholt!, Masnedsund ; Am. Klervermarken ; B. (ROedd^^^) Sisymbrium 

 sinapistrum. J. Aalborg (Uhrenholt); S. Gl. Kalkbrxnderivej ; Amager. Sisym- 



