THE FUNGI WHICH CAUSE PLANT DISEASE 485 



P. tabifica Prill is perhaps identical with Myeosphserella tabifica, 

 though Potebnia " questions this. See p. 247. 



P. maculiformis (Pers.) Sacc. on chestnut =Mycosph£erella 

 maculiformis. See p. 249. 



P. soUtaria E. & E.^- « 



Perithecia minute, immersed, the ostiole only erumpent; conidia 

 broadly elliptic, 8-10 x 5-6 m, surrounded by a mucilaginous sheath. 



It is the cause of apple fruit blotch and of cankers and leaf spots. 

 On the fruit it was first reported by Clinton ^ in 1902. The fruit 

 spots show a characteristic fringed appearance owing to the 

 imequal advance of the mycelium which is limited to the outer- 

 most fruit cells. In the fruit the pycnidia develop subepidermally. 



Fig. 336. — P. solitaria. 1-month-old colony on apple agar. After 

 Scott and Rorer. 



The fimgus was grown in pure culture and its identity on twig, 

 leaf and fruit was shown by cross inoculation. 



P. persicae Sacc. is common on peach leaves. 



P. piricola Sacc. & Speg. is foimd on apple and pear. 



P. limitata Pk.'" is reported as the cause of an apple leaf spot. 



Spots round minute, 2-6 mm., brown or reddish; pycnidia epiph- 

 yllous, black, few, punctiform; spores ellipsoid, 7-8 x 4 jn. P. mail 

 P. & D. occurs on apple and pear. 



P. pirina Sacc." 



Spots variable; pycnidia epiphyllous, punctiform, lenticular, 

 100-130 M, context loosely cellular, brown; conidia ovoid to 

 ellipsoid, 4-5 x 2-2.5 /i. 



This was long regarded as the chief factor causing the common 

 leaf spot on the apple and pear. Recent work throws doubt on this. 



