476 



FUNGI IMPERFECTI. 



of the shoots, aud either rupture the epidermis or grow out from 

 the leaf -scar cushions (Fig. 297). The couidia are abjointed 

 from filamentous conidiophores inside the pycnidia, and emerge 

 as tendril-like structures. They are two-celled, small, cylindrical, 



and pointed at both ends. 

 Germination takes place 

 easily in water, and the 

 disease spreads rapidly over 

 the young developing shoots 

 during May. The mycelium 

 permeates the twig, living 

 both inside the cells and 

 between them. 



The disease has been 

 observed on Picea excelsa 

 and F. Menziesii, not only 

 in nurseries and on young 

 trees, but also in pole- 

 forest, where it frequents 

 the upper crown and causes 

 death. At the beginning 

 of an attack the pruning 

 of diseased twigs in young 

 plantations should be at- 

 tended to. 



Septoria nibi (Westend.).^ Blackberry leaf-spot. This is a 

 parasite of some economic importance in the United States, where 

 it interferes with the blackberry culture. It also occurs in Europe 

 and Britain. 



S. ribis Desm. produces a somewhat similar disease on leaves 

 of currant and gooseberry.^ (Britain and U.S. America.) 



S. piricola Desm. occurs throughout all Europe, causing little greyish 

 spots on leaves of pear trees. It is probably a pycnidial form of Sphaerella 

 lucillae Sacc. 



S. crataegi Kich. A common species on leaves of Crataegus in Europe. 



S. cerasina Peck. On leaves of Prunus serotina in the United States. 



Many forms of Septoria infest cultivated vegetables : 



S. petroselini Desm. is the cause of dry spots appearing on leaves of 



^Description in Bulletin, No. 6, Ohio Agric. Exper. Station, 1891. 

 "Description in Bulletin, No. 13, Iowa Agric. Exper. Station, 1891. 



Fig. 296. — Seploria parasitica, a. Young diseased 

 shout of Spruce, with apex still fresh and green. 

 b. Needle diseased towards base, c, Apex of a two- 

 year^)ld shoot, into which the disease has extended 

 backwards from the younger shoot ; the brown 

 discoloration of cortex and pith is indicated by 

 shading. (After R. Hartig.) 



