496 FUKGI IMPERFECTI. 



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 Hnes. 

 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 pyenidia-like structures without a peridium, arising 

 from a stroma 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. nigra. 

 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 Fhleospora, as 

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

 mentous, and pluricellular. 



Amongst the more important North American species are : 



S. profasum (E. et E.). On living leaves of Coryliis 

 americana. 



S. fraxini Hark. On Fraxinus Oregana. 



S. apocyni Peck. On Apocynum cannabinum. 



III. HYPH0MYCETE3. 



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. 



