THE FUNGI WHICH CAUSE PLANT DISEASE 245 



The slender mycelium pervades the diseased areas disorganizing 

 the host cells and resulting in reddish coloring of the sap. Ob- 

 servations of Dudley "* indicate that the mycelium or portions of 

 it can remain alive over winter in the host tissue ready to produce 

 abundant conidia in the spring. 



The most abundant conidial stage is the Ramularia-form 

 (Fig. 179) which abounds all summer. Sowings of these conidia, 

 under conditions of humid atmosphere, result in characteristic 

 spots in from ten to eighteen days. Toward winter sclerotial 

 bodies are formed from the mycelium. These in culture dishes 

 have been seen to produce the typical summer conidia. Some of 

 these sclerotia-like bodies have been reported as "spermogonia," 

 bearing numerous "spermatia" 1x3 fi. Perithecia abound in au- 

 tumn. These are larger than the spermogonia and are usually 

 embedded in the leaf tissue, though they sometimes appear super- 

 ficially. Conidiophores are often borne directly on the perithecium 

 wall. Ascospores germinate within the ascus. From the mycelium 

 resulting from ascospores Dudley ^'* observed the formation of 

 typical summer conidia. 



M. grossularise (Fr.) ^^ 



Perithecia hypophyllous, gregarious, spherical, with minute 

 ostiole, black; asci short-pedunculate, clavate, 55-66 x 8-12 fi; 

 spores fusoid, filiform, curved or straight, uniseptate, hyaline, 

 26-35 X 3^ fi. 



It has been reported on the gooseberry associated with Cer- 

 cospora angulata and Septoria ribis. 



M. rubina (Pk.) Jacz.^" 



Perithecia minute, gregarious, submembranous, obscurely papil- 

 late, subglobose or depressed, erumpent, black; asci cylindric, 

 subsessile, 70-80 x 10-12 ju; spores oblong, obtuse, uniseptate, 

 generally constricted in the middle, 15 x 6-7 /x, upper cell broadest. 



Conidia (=Phoma) are associated with the perithecia and are 

 supposed to be genetically connected with them as is also a second 

 spore form ( =Coniothyrium). 



The species is held responsible for bluish-black spots on rasp- 

 berry canes. 



M. cerasella Aderh.^^ is reported as the perithecial stage of 

 Cercospora cerasella common on cherry. 



