WHITE EUSTS. 137 



spurry {Spergiilaria mbra) by Mr. R. Gr. Keeley^ in 

 Swanscombe Marshes (September_, 1864). Of tbe 

 other species it is not improbable that one or two 

 may yet be found in this country. Without at- 

 tempting to indicate their microscopic differences, 

 it may be serviceable to name the species of 

 phanerogamic plants on which they are likely to 

 be found. The Purslane white rust {Cijstopiis For- 

 tulaccBy D. C.) should be sought on the purslane, 

 which, though of limited cultivation, is exceedingly 

 liable to attack from this parasite, and the Thistle 

 white rust {Oystopus spinulosiiSy D. By.) may pro- 

 bably be met with on the leaves of the common 

 thistle {Oniciis arvensis) or some of its allies. 



Considerable interest is now attached to these 

 parasites, which, as far as we at present know, 

 differ materially in their reproduction from the 

 other dust-like or uredinous fungi with which they 

 have long been associated. Dr. de Bary proposes 

 the union of these with the mould-like fungi of the 

 genus Peronospora, to which the mould infesting 

 the potato belongs, so as to constitute by them- 

 selves a group apart from the genera with which 

 both have heretofore been associated. Whether 

 his views will be accepted by mycologists time will 

 speedily prove. Under any circumstances, micro- 

 scopical and botanical science will reap considerable 

 benefit from his researches. 



