SPHAERELLA 197 



Pear leaf fleck {Sphaerella sentina, Schrot.). This fungus 

 has long been known as Septoria piricola (Desm.), but 

 Klebahn has recently demonstrated that the Septoria is only 

 a conidial form of Sphaerella, an ascigerous genus. The 

 conidial condition forms numerous small, greyish-white 

 specks, most obvious on the upper surface of the living 

 leaves. When the leaves are dead the ascigerous condition 

 of the fungus appears under the form of minute, scattered, 

 or crowded, blackish points. Most frequent on pear leaves, 

 although occurring on apple leaves also. 



Septoria stage. Minute black perithecia scattered on small 

 bleached spots on living leaves. Conidia elongated, slender, 

 curved, pale olive, 55-60X3-4 p, escaping in a tendril. 



Sphaerella form. Perithecia partly immersed, papillate, asci 

 cylindrical, spores i-septate, resembling two cones joined by 

 their bases, pale olive, 15X5 /*. 



When severely attacked the leaves fall early in the season 

 and affect the crop. An important point is to collect and 

 burn infected dead leaves, as the spores on these start the 

 disease the following season. 



Klebahn, Zeitsch. fiir Pflanzenkr., 18, p. 5 (1908). 



Blight of cereals. It often happens that after a period 

 of dry weather followed by more or less continuous rain, in 

 the month of June, that wheat and other cereals assume a 

 yellow tint, followed by a shrivelling and bleaching of the 

 leaves which become covered with little, blackish, olive tufts, 

 which are the clustered conidia-bearing branches of a fungus 

 best known in this country under the name of Cladosporium 

 herbarum (Pers.), but which in reality is a conidial form of 

 Sphaerella Tulasnei (Janczewski). In many instances the 

 plants are killed outright, leaving bare patches here and 

 there in the field, or a thin crop is the result. At other 

 times when the disease appears later in the season, the grain 

 is attacked and covered more or less with the fruiting bodies 

 of the Cladosporium stage, which give to it a blackened 

 appearance. Such grain imparts to flour a very unpleasant 

 flavour. I have shown elsewhere that the forms called 

 Dematium pullulans and Hormodendron cladosporoides are 

 respectively conditions only of Cladosporium herbarum. 

 Janczewski arrived independently at the same conclusion, 

 and in addition, by means of pure cultures, proved 



