484 



THE FUNGI WHICH CAUSE PLANT DISEASE 



epidermis, lenticular to globose, thin membranous, opening by 

 a pore; conidia small, ovate to elongate, continuous, hyaline or 

 green; conidiophore short or almost obsolete. On leaves. 



In part =Guignardia, Valsonectria, Mycosphserella. 



The genus is a very large one of some eight hundred forms, few of 

 which have been adequately studied. It differs from Phoma only in 

 that it is foliicolous while Phoma is caulicolous, a distinction which 



Fia. 335. — P. solitaria. 1, section through apple; 4, spores 

 from apple blotch showing appendages; 6-7, germinating 

 spores; 9, mycelium from corn-meal cultures. After Scott 

 and Rorer. 



is not consistently maintained and which is untenable for generic 

 limitation (see p. 478). 



The fungus produces leaf spots by killing or weakening the 

 leaf tissue with its mycelium. The spots are circular or subcircular, 

 unless rendered angular by obstruction by veins, and the pycnidia 

 may usually be seen with a lens in old spots unless the color of the 

 leaf forbids. Similar effects follow on fruits. 



P. ampelopsidis E. & M. on Ampelopsis is probably identical 

 with P. labrusc«=Guignardia bidwellii. See p. 238. 



P. bellunensis Mart, on elm =Mycosphaerella ulmi. See p. 249. 



P. brassicse (Carr.) West on cabbage, etc. =Mycosphserella bras- 

 siaecola.^ See p. 249. 



P. labruscse Thum. on the grape =Guignardia bidwellii. See 

 p. 238 



