Relation between Host and Parasite 23 



that by means of the asterisk prefixed to the plants in the host- 

 index attention will be directed to this point, and so lead mycol- 

 ogists to clear up these doubtful records. The work is difficult, as 

 it consists in many cases in proving that a certain species does not 

 grow on a certain host-plant; this can only be hoped to be ac- 

 complished by continued observations for many years, at the end 

 of which time it might be safe to disregard many published 

 records. 



One curious source of error still remains to be noticed. It 

 has, up to the present, been generally supposed that it is a safe 

 practice to consider pcrithecia found on any host -plant as originat- 

 ing there. Many cases that have come under consideration prove 

 that this is not so. In some instances stray perithecia of certain 

 species occurring on strange hosts have been published as new 

 species. This is the case with '' Erysiphdla Carcstiana^'' which 

 was founded on perithecia of Phyllactinia corylca accidentally 

 adhering to the pileus of Fomcs foincntarins. ** Uncinida Co- 

 t(7nlna?ia'' is, I believe, merely U. salicis on the leaves of Scu- 

 tellaria^ and ^^ Erysiphe vitigera'' appears to have been established 

 on stray perithecia of E, cichoraccanim^ occurring on the vine. 

 Similiar cases, mentioned in detail under the respective species are 

 the following : Uncinida salicis on Artemisia vulgaris^ U, pninastri 

 on Lonicera Xylostciun^ U. Delavayi on Celtis^ Phyllactinia corylca 

 on probably many herbaceous hosts and Microsphacra alni on Pop- 

 tdus grandidcntata, Uncinida gcniculata has occurred appar- 

 ently accidentally on Hydropliyllum appotdiculatum. I have 

 seen, in herbarium specimens, Podosphaera tridactyla adhering 



r 



in a tangled mass to a leaf of Fagiis sylvatica, and perithecia of 

 Phyllactinia corylca accidentally present on a rose leaf. A few 

 perithecia oi Microsphacra alni have been seen among those of M. 

 diffusa on a leaf of Dcsmodiiun panicidatum, and, also, in a speci- 

 men named M, grossulariae, adhering to the margins o{ goose- 

 berry leaves. 



The accidental presence of perithecia on plants may perhaps 

 be accounted for in some cases by the rubbing together of dried 

 specimens in herbaria, or possibly by the repeated use of the same 

 drying paper to which perithecia would adhere, in pressing the 

 leaves. 



