186 THE FUNGI WHICH CAUSE PLANT DISEASE 



(but not always) more or less closely 3 to 6-times dichotomously 

 branched, tips of ultimate branches regularly and distinctly re- 

 curved; asci 3-8, ovate to ovate-globose, 42-70 x 32-50 m, usually 



but not always short stalked; 4 to 

 8-spored; spores 18-23 x 10-12 fi. 



This species is the most variable of 

 the Erysiphese showing large latitude in 

 number of spores in the ascus, in length, 

 color and branching of appendages, in 

 Fig. 136.— m. aini, appendage size of perithecia. It occurs upon Very 



tips. After Salmon. , , ,^11. 



numerous hosts. The economic ones on 

 which it is most common are: Syringa, Lonicera, Alnus, Betula, 

 Quercus, Carya, Castanea, Juglans, Platanus. 



It is confined to the northern hemisphere. 



Salmon recognizes in addition to the typical form six varieties. 

 Those of economic importance are: 



(a) extensa (C. & P.) Salm., a robust form on various American 

 species of oaks; 



(b) calocladophora (Atk.) Salm., also a robust form on American 

 oaks but having pseudo-trichotomously branched appendages 

 and large spores; 



(c) vaccinii (Schw.) Salm., in America on Catalpa and various 

 genera of Ericaceae is a small-spored, long-appendaged form. It 

 includes M elevata on Catalpa; 



(d) lonicerae (D. C.) Salm., on species of Lonicera in Europe. 

 M. diffusa C. & P. 



Amphigenous; mycelium persistent, thin and effused, or sub- 

 persistent and forming vague patches, or quite evanescent; peri- 

 thecia scattered or gregarious, globose-depressed, very variable in 

 size, 55-126 fi in diameter, averaging 90-100 ii, cells 10-20 At 

 wide; appendages very variable in number and length, 4-30, or 

 rarely crowded and as many as 50, 13^ to 7-times the diameter of 

 the perithecium, smooth, aseptate or 1 to3-septatein the lower half, 

 colorless or pale brown towards the base, flaccid when long, thin- 

 walled above, becoming thick-walled towards the base, apex 3 to 5- 

 times dichotomously or subdichotomously divided, branching dif- 

 fuse and irregular, branches of the higher orders sub-nodulose, 

 often apparently lateral, tips of ultimate branches not recurved; 



