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 Oidium 

 monilioides before its relationship was known, but undoubtedly 

 this is only the conidia of Erysiplie f/raminis. In like manner 

 the vine disease (Oidium Tuckeri) is most probably only the 

 conidia of a species of Erysiphe, of which the perfect condition 

 has not yet been discovered. On roses the old Oidium leuco- 

 ctfniu-m is but the conidia of Spfuerotheca pannosa, and so 

 of other species. The Erysiphe which ultimately appears on 

 the same mycelium consists of globose perithecia, externally 



PIG. 103. Erysiphe cichoracearum. o. Receptacle ; o. mycelium. (De Bary.) 



furnished with thread-like appendages, and internally with usci 

 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 Oidium, the asci contained in 

 the sporangia, which is the proper fruit of the Erysiphe^ 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. 



