II Mil [MPERFECTl 



353 



experiments suggest that Sphceropsis Mali (\\ r est) Sacc. on bark, 

 Spkaropsis ciucrca (C. & E.) Sacc., and Splucropis Malomm Pk. 

 are properly the same fungus. Until, however, more careful com- 

 parisons shall have been made, we may continue to refer to this 

 disease-producing fungus as Sphceropsis Malorum. It may be, 

 moreover, that it occurs upon many other hosts. 



The fungus. The mycelium is sooty brown or olivaceous 

 within the tissues. It penetrates the bark readily but mav not 



tfQSrt- 



FIG. 171. SPHCEROPSIS MALORUM : MATURE PYCNIDIUM. (Photograph 

 of a drawing by F. C. Stewart) 



extend far into the wood. The pycnidia are erumpent, usually sur- 

 rounded by a broken epidermis (Fig. 171), and they appear in 

 cross section somewhat depressed-conical at the apex. The spores 

 are oblong-elliptical, brown, and usually about twice as long as 

 bro*ad, measuring in general 22-32 x 10-14 /x. It has been found 

 that the average sizes of the spores of the forms on apple, pear, 

 and quince vary according to the host and part attacked. The most 

 noteworthy difference is that upon the limbs the spores are smaller 

 than on the fruits. The spores seem to retain their vitality for a 

 considerable period of time, having been germinated after being 

 stored for a year in the laboratory. On agar the fungus develops 



