412 E. S. SALMON ON THE ERYSIPHACE2E. 



throughout the group of Hyphomiycetes such thin-walled spores are 

 the usual means of carrying the fungus through the winter. 



The second gap in our knowledge of the life-history is associated 

 with the subject of the connection of the fungus and its host- 

 plant. In Professor Magnus' experiment of sowing conidia of the 

 Hop Mildew [Sjyhcerotheca Humuli) on leaves of the Dandelion — 

 a host upon which in nature the perithecial form has never been 

 found — only the conidial or Oidium-iovm of fruit was produced. 

 It is extremely probable that on some host-plants the fungus has 

 lost, or not yet acquired, the power of continuing its development 

 up to the perithecial stage, as in the case of the common Oidium 

 on species of Myosotis, Oidium Chrysanthemi, etc. Valuable 

 scientific work can be done by any one with opportunities for 

 working in the field, by taking a mildew from one species of 

 host-plant, and attempting to grow it on other species. 



In conclusion, we see that in our knowledge of the life-history 

 of the Erysijyhacece two great gaps exist : in the first place, we 

 do not know in what way every spring the ascospores give rise to 

 the conidial (Oidium) stage; secondly, we do not know to what 

 extent each foim of mildew is limited in its choice of host-plants, 

 and whether the same species on different host-plants may not 

 exhibit slight morphological characters correlated with its occur- 

 rence on those plants. At present these gaps in our knowledge 

 are filled by hypotheses, — to substitute facts for these should be 

 our aim. 



Joimi. Qv.ekett Microscopico.l Club, Ser. 2, Vol. VII., No. 47, November IfOO. 



