246 



THE FUNGI WHICH CAUSE PLANT DISEASE 



FiQ. 180. — M. sentina, Septona stage. 

 Portion of a section through a pear leaf 

 spot, showing e, e, epidermis; p, pali- 

 sade cells sp, spongy parenchyma; o, 

 S. piricola pycnidium, giving out 

 spores, b. After Longyear. 



M. sentina (Fr.) Schr. 



Perithecia, 80-110 /i; on dead spots of leaves, the long ostiole 

 erumpent; asci clavate, 60-75 x 11-13 fi, colorless; spores fusiform, 



curved or straight, 26-33 x 



Conidia (=Septoria piricola) 

 borne in pycnidia which are 

 similar in size and form to the 

 perithecia; conidia fi 1 i f o r m, 

 curved, 3-celled, 40-60 x 3 /i. 

 On pear and apple. 



The conidial form was men- 

 tioned in America as early as 

 1897 by Atkinson ^^ and was 

 the subject of a comprehensive 

 bulletin by Duggar in 1898.^* 

 The ascigerous stage was demon- 

 strated by Klebahn in 1908.2''2 

 The pycnidia, mainly hypophyllous, are sunk deeply into the 



leaf tissue and are surrounded by a delicate pseudoparenchyma. 



The conidia are distinctly tinted, green or smoky. 

 The perithecia are nimaerous, and crowded on grayish spots, 



hypophyllous, on old wintered leaves. They are without stroma. 



Klebahn by inoculations (June, 1904) with ascospores secured 



spots in fifteen days and pycnidia in twenty- 

 nine days, bearing the characteristic conidia. 



From ascospores he also made pure cultures 



which soon developed pycnidia with conidia. 



Pure cultures made from conidia in the hands 



of both Klebahn and Duggar have failed to 



give typical perithecia. 

 M. citruUina (C. 0. Sm.) Gros. 

 Perithecia roughish, dark-brown or black, 



depressed-globose to inverted top-shaped, 



usually with a papillate ostiole, densely 



scattered, erumpent, 100-165 n; asci cylindric to clavate, 45-58 x 



7-10 /J.; spores hyaline, oblong-fusoid, constricted at the sep- 

 tum. 



Fig. 181. — M. sentina. 

 Conidial layer, co- 

 nidiophores and co- 

 nidia. After Kle- 

 bahn. 



