242 THE FUNGI WHICH CAUSE PLANT DISEASE 



oculations under all conceivable conditions, failed utterly of posi- 

 tive results. 



From the Caucasus Prillieux and Delacroix "^ have described a 

 Guignardia causing a black rot of grapes which is regarded as 

 distinct from the usual American form, differing both in the peri- 

 thecial and conidial stages. This is called G. baccae (Cav.) Jacz. 

 Its conidial form Phoma reniformis eventually covers the whole 

 berry with pustules. Two kinds of pycnidia 

 are described. 

 G. vaccinii Sh."^- "^ 



Perithecia on young fruit or flowers, sub- 



epidennal, globose, walls thick, carbonous; 



asci clavate, 60-80 m long; spores elliptic 



or subrhomboidal, hyaline, becoming tinted. 



^, . Conidia (=Phyllosticta) borne in pycnidia 



Fig. 177.— A vertical sec- similar to the pcrithecia but thinner-walled, 



ofouiUrlS'vaccinii! 100-120 M! conidia hyaline, obovoid, 10.5- 



showing ascl. After ]3 5 x 5-6 ft. On Vaccinium. 



In the decaying berries all sporing forms 

 of the fungus are rare though in the softened tissues fungous 

 hyphse abound. Transferred to culture media these hyphffi grow 

 readily and produce spores abundantly. 



The conidial form is conmion in artificial culture; the peri- 

 thetical form comparatively rare. Pycnidia on leaves are sub- 

 epidermal, usually hypophyllous, and are quite abundant. The 

 spores at maturity issue in coils from the ostiole. 



The fungus was studied extensively in artificial culture by Shear, 

 wet sterilized commeal proving a most suitable medium. Pycni- 

 dia appeared in four to eight days after inoculation and spores were 

 mature at twelve to eighteen days. Both pycnidia and perithecia 

 were obtained in pure cultures. The rarity of cultures able to pro- 

 duce perithecia is explained by Shear on the assumption "that 

 there is some inherent potentiality in the mycelium of the fungus 

 in certain strains, races, or generations which causes it to produce 

 the ascogenous stage whenever conditions for its growth are favora- 

 ble, i. e., on favorable culture media without special reference to 

 their exact composition or environment or on the leaves of its nat- 

 ural host." Conclusive infection experiments have not been made. 



