156 A Monograph of the Erysiphaceae 



Var. extensa is a robust form produced on certain species of 

 oaks, and in its extreme state is very distinct in the long flaccid 

 appendages. The apical branching does not deviate from the or- 

 nate type commonly found in American examples of M. alni on 

 oaks. The spores appear to be distinctly larger. A complete 

 series of intermediate forms exist connecting this variety with the 

 type. 



Var. calodadophom is another robust form, similarly confined 

 to certain American oaks. The distinguishing character is the 

 axial elongation shown in the apex. of mpst appendages. The 

 spores are large. Connecting links, both on the side of the vari- 

 ety and of the type, are occasionally found. 



Var. vaccinii differs from the two varieties mentioned above 

 in the smaller spores, and in the variable nature of the apical 

 branching of the appendages. The long, thin appendages and 

 usually looser apex distinguish it from the type, although as the 

 appendages tend to become shorter, they become stouter, with the 

 apical branching more approaching that of M. alni. Certainly 

 allied to the European var. divaricata. 



Var. Indcns occurs on Vicia Americana, and is known at once 

 by the more or less contorted appendages, with very lax and vari- 

 able apical branching. The tips of the ultimate branches are very 

 frequently straight. 



The two European varieties are loniccrae and divaricata. 



Var. loniccrae.— T\\is has perhaps some claim to be consid- 

 ered a distinct species which has been evolved on species of Loni- 

 cera in Europe, perhaps in the same way as M. berbcridis has on 

 Berberis; to this species, indeed, the present variety shows some 

 affinity. On the other hand, relationship with M. alni is shown 

 in the fact that the characteristically straight tips of the var. loni- 

 cerae are occasionally recurved as in this species. 



Var. divaricata.— T\{\% has hitherto been supposed to be con- 

 fined to Rhammts Frangida : a single occurrence, however, on Lon- 

 iccra nigra has been noted. In its extreme form this variety is very 

 different from any European forms of Jf. alni in the long, divergent, 

 usually reflexed branches of the apex of the long appendages. 

 Occrasionally, however, the appendages are shorter, and the apical 

 branching more like that of M. alni. Intermediate forms also 



