496 FUKGI 1MPERFECTI. 



itself in the drying- up of young twigs before their buds open 

 in spring. The older branches, however, assume their normal 

 foliage. Examination of diseased twigs reveals the mycelium 

 of a parasitic fungus living both inside and between the 

 cells of rind and wood. Conidial patches break through 

 the host's epidermis about May as long greyish-green lines. 

 The conidia are hyaline, three-celled, and cylindrical with 

 rounded ends ; the conidiophores are short thick rods. In May 

 and June the spores are capable of infecting new hosts, and 

 germinate in a few hours. Infection of twigs takes place in 

 summer, and the mycelium spreads through the first-year 

 shoots, without, however, giving any external indication of its 

 presence till the following spring, when the twigs dry up as 

 already described. 



S. ulmi (Fr.) may be a form of Phyllachora ulmi. The 

 mycelium lives in parenchymatous cells, and causes the formation 

 of brownish-yellow spots on leaves of the elm. The conidial 

 patches form tiny points on the lower surface of the leaf: they 

 consist of pycnidia-like structures without a peridium, arising 

 from a stroina developed under the epidermis. The conidia are 

 spindle-shaped and pluricellular. 



S. mori (Lev.) is stated by Briosi and Cavara to produce yellow 

 spots with brown margins on the leaves of Morns alba and M. ni<ii-. 

 Death and premature defoliation of the host then take place. 

 The conidial patches develop under the epidermis, and rupture 

 it as the conidiophores emerge ; they have no real peridium, 

 hence the fungus cannot belong to the group Phlcospora, as 

 Saccardo supposed. The conidia are long, cylindrical or fila- 

 mentous, and pluricellular. 



Amongst the more important North American species are : 



S. profusum (E. et E.). On living leaves of Cori/ln* 



S. fraxini Hark. On Fm.rinus Orcgaun. 

 S. apocyni Peck. On Apocynum 



III. HYPHOMYCETES. 



Conidia produced neither in pycnidia as in Sphaeropsideae, 

 nor from a special stroma as in Melanconideae, but free on 

 conidiophores given off from the mycelium. 



