262 



ASCOMYCETES. 



a cloud of spores so ejected may easily be seen. Infection 

 takes place on the birch flowers. It is possible to promote 

 germination in water and on moistened leaves, but the germ- 

 tubes soon die. 



This disease, on account of the small size of the birch fruit 

 and the tiny sclerotia, remained for a long time quite un- 

 observed, yet it seems to be common everywhere ; in Eussia it 

 has been found frequently, also in Germany, North America, 

 and Japan. It possesses considerable economic importance, 

 since diseased seeds are no longer capable of germination. 



Fro. 139. — Sclei'otinia betulae. a, Birch fruits with sclerotia, which have 

 germinated and formed cup-like apothecial discs ; rhlzoids have developed on 

 the stalks. &, Birch fruit, somewhat enlarged, with semilunar sclerotia. (After 

 Nawaschin.) 



Hormomyia betulae Wtz. often occurs along with the above. 

 It causes the production of thick spherical fruits with little or 

 no wing. Sclerotinia adusta Karst. has also been found on 

 birch leaves in Finland. 



Scl. alni Naw. Woronin found this first on catkins of 

 Alnus incana. Nawaschin has more recently investigated it.^ 



Scl. rhododendri Fischer.^ This was first discovered by 

 Fischer in 1891 in fruits of the Alpine-rose (Rhododendron 

 ferrugineum and B. hirsutum) in Switzerland. It has since 

 been observed in various parts of Switzerland and the Tyrol. 



1 Nawaschin, Berichte d. devisch. hotan. Oes., 1894; Maul, ffedioigia, 1894, 

 p. 213. With two plates. 



^E. Fischer, Nahirforsch. Ges. Bern, 1891 ; also Benchte d. schweiz. hotan. Ges., 

 1894. With figures. 



