502 



THE FUNGI WHICH CAUSE PLANT DISEASE 



About two hundred species several of them important plant 

 pathogens. 



S. malorum Pk. «°' "■ ""'^ 



Mycelium sooty-brown; pycnidia erumpent, usually surrounded 

 by broken epidermis, apically somewhat depressed; conidia oblong 

 elliptic, broAvn, usually about twice as long as broad, 22-32 x 10-14 

 H, varying in size with host and part attacked. 



On apple, pear, quince, hawthorn; on twigs causing canker or 

 blight; on fruit causing rot and on leaves causing spots. 



iiu. 34S. — S. malorum, 6, dark colored mycelial 

 threads among the cells of the fruit; d, a 

 pycnidium, which has pushed through tlie epi- 

 dermis, c, and is giving off dark colored spores, e; 

 Bf mature spores germinating in water. After 

 Longyear. 



This is one of the common causes of pomaceous fruit rots and 

 of leaf spot in the United States. Its occurrence in leaf spots was 

 noted in 1898," and in 1902 Clinton *° recognized it as their cause. 

 Cultures were obtained from diseased leaf spots bj^ Scott & Rorer "° 

 and by inoculations the ability of the fungus to cause spots was 

 definitely proved. 



This fungus was reported by Paddock ^^ as the probable cause 

 of apple twig blight and canker and cross inoculation between 

 twigs and fruit proved the identity of the fungus on these two parts. 



The mycelium is very dark or olivaceous and abounds in the 

 rotten pulp of affected fruit, also in diseased bark, and is even 



