THE FUNGI WHICH CAUSE PLANT DISEASE 203 



cambium. On this host, however, it is now said to be non- 

 parasitic.^^' 



Durand,^^* culturing the conidial form on sterile currant stems, 

 observed the formation of tubercles with abundant conidia after 

 about fourteen days. On agar conidia were produced directly from 

 single hyphae without any stroma. Perithecia were found in the 

 field on the tubercles with the conidia in February. 



N. ditissima Tul. 



Stroma light colored; perithecia cespitose, densely and irregu- 

 larly clustered, or rarely scattered, ovate, ostiole prominent, bright 

 red, smooth or roughened; asci cylindric to clavate, 80-90 x 8-10 /x; 

 spores fusoid, 12-16 x 4^5 ix. 



The unicellular microconidia are followed by falcate, multi- 

 cellular, macroconidia (Fusidium candidum), which are borne on 

 pale stromatic cushions. 



Common on dicotyledonous trees, especially beech, oak, hazel, 

 ash, alder, maple, Ume, apple and dogwood, where it is usually a 

 wound parasite, particularly common after hail. It is especially 

 well known from Europe " and has more recently attracted atten- 

 tion in America. 



The mycelium does not usually advance more then one centi- 

 meter in each year. It is beUeved that it can travel within the 

 wood and break through the cambium and cortex at points some 

 distance from the place of original infection, thus producing new 

 spots. Very minute conidia produced in the bark aid in tissue de- 

 composition. White conidial (Fusidium) stromata appear near 

 the periphery of affected spots and here, too, in groups or scattered, 

 appear the deep red perithecia. 



N. cucurbitula Sacc. 



Perithecial clusters erumpent, often irregular in form, 1-2 mm. 

 in diameter; perithecia densely clustered, bright red, ovate, with 

 a prominent ostiole, rarely collapsing; asci cylindric to clavate 

 75-100 X 6-8 m; spores at first crowded and partially 2-seriate, 

 finally becoming 1-seriate, lying obliquely in the ascus, broad, 

 fusoid, rarely subelliptic, 14-16 x 5-7 m- 



Its hosts are spruce, fir, pine and other conifers in Europe and 



North America. . 



The fungus is usually a wound parasite, often following hail. 



