THE FUNGI WHICH CAUSE PLANT DISEASE 137 



Fig. 91.— S. urnula, 

 monilifoTin conidia 

 with disjuDctois. 

 After Woronin. 



possess Botrytis forms (see pp. 141 and 578), others Monilia (see 



pp. 139 and 558) forms of conidial fructification. In addition to 



these there may be gonidia, which appear to be 



degenerate, f unctionless conidia. In some species 



there is no known spore form except that in the 



ascus. 



S. ledi Now. is of especial interest as the one 

 .fungus outside of the Uredinales that exhibits 

 hetercecism.^^^ 



Many forms found upon separate hosts and 

 presenting shght differences under the micro- 

 scope, often even no microscopic differences, 

 have been named as separate species. Only 

 long careful culture studies and inoculation ex- 

 periments will determine which of these species 

 are valid, where more segregation, where more 

 aggregation is needed. 



The mere association of Botrytis or Monilia 

 conidial forms with Sclerotinia, in the same host, 

 has repeatedly led to the assumption that such forms were genetic- 

 ally connected. Such assumptions are not warranted. Only the most 

 careful study and most complete evidence justify such conclusions. 



The genus contains some fifty species which are divided into two 

 subgenera; Stromatinia Boud., forming sclerotia in the fruits of 

 the host; Eusclerotinia Rehm forming sclerotia in or on stems 

 and leaves of the host. 



When conidia are known those of Stromatinia are of the Monilia 

 type and those of Eusclerotinia of the Botrytis type. Each group 

 contains important economic species. 



S. fructigena, S. cinerea and S. laxa.^"- "• ^s. 291-295 



These forms are perpetuated chiefly by their conidia. The 

 ascus-forms are much less often seen. 



When the conidia fall upon the peach, the mycelium develops 

 and penetrates even the soimd skin, then rapidly induces a brown 

 rot. The mycelium within the tissue is septate, much branched, 

 and light brown in color. It soon proceeds to form a subepidermal 

 layer and from this the hyphae arise in dusty tufts of Monilia-form 

 conidiophores and conidia (Fig. 92). The earlier conidia are thin- 



