POLYMORPHISM. 191 
authenticated polymorphy prevails. These fungi are developed 
on the green parts of growing plants, and at first consist of a 
white mouldy stratum, composed of delicate mycelium, on which 
erect threads are produced, which break up into subglobose 
joints or conidia. The species on grass was named O/dium 
monilioides before its relationship was known, but undoubtedly 
this is only the conidia of Erysiphe graminis. In like manner 
the vine disease (Oidium Tuckeri) is most probably only the 
conidia of a species of Hrysiphe, of which the perfect condition 
has not yet been discovered. On roses the old Otdium leuco- 
conium is but the conidia of Spherotheca pannosa, and so 
of other species. The Erysiphe which ultimately appears on 
the same mycelium consists of globose perithecia, externally 
Fic. 103.—Erysiphe cichoracearum. u. Receptacle; 0. mycelium. (De Bary.) 
furnished with thread-like appendages, and internally with asci 
containing sporidia. In this genus there are no less than five 
different forms of fruit,* the multiform threads on the mycelium, 
already alluded to as forms of Ozdiuwm, the asci contained in 
the sporangia, which is the proper fruit of the E'rys/phe, larger 
stylospores which are produced in other sporangia, the smaller 
stylospores which are generated in the pycnidia, and separate 
sporules which are sometimes formed in the joints of the neck- 
laces of the conidia. These forms are figured in the “ Introduction 
* Berkeley, ‘‘Introd. Crypt. Bot.” p. 78, fig, .20. 
