CULTURAL CHARACTERS. 15 



observed similar appendages on the spores of Phyllosticta minima 

 (B. & C.) E. & E., the fungus which causes the common maple leaf- 

 spot. 



'The pycnospores, which are produced in great abundance on young 

 green fruits until nearly midsummer, germinate readily and under 

 favorable conditions may reinfect the fruits, twigs, and leaves. As 

 the fruit approaches maturity spore production ceases, although 

 pycnidia-like bodies continue to be formed. It is possible that this 

 is an attempt on the part of the fungus to produce an ascigerous 

 stage, but an examination of a great quantity of diseased fruits both 

 in the fall and in the following spring has failed to reveal any asci. 

 The coneeptacles are filled with irregular cell-like bodies rich in pro- 

 toplasm, which may be abortive asci. 



The growth of the fungus on the twigs is confined to the bark, 

 where it kills the tissues and forms the cankers previously described. 

 The formation of pycnidia begins soon after the cankers are visible 

 and continues throughout the season as the cankers increase in size. 

 These pycnidia produce spores in great abundance which are similar 

 in all respects to those from the fruit and, like them, as shown by 

 inoculation experiments, may infect fruit and leaves. The fungus 

 is perennial in the cankers, enlarging the diseased areas from year to 

 year. 



CULTURAL CHARACTERS. 



The fungus grows well on nearly all ordinary culture media, such 

 as potato, apple, prune, and corn-meal agar, sterilized potato cylin- 

 ders, beans, rice, corn meal, and apple twigs. On agar the vegetative 

 growth is quite characteristic, producing an irregular dark gray mass 

 of mycelium, which in its compact radiating appearance suggests the 

 blotches on the fruit. (PI. Ill, fig. 10.) The fungous growth is very 

 dense but quite restricted. The mycelium is for the most part em- 

 bedded in the agar and is greenish black, but the fungous mass has a 

 grayish appearance on account of tufts of short, hyaline hyphae, which 

 are produced over the surface. On apple wood, rice, and corn meal 

 the growth is more extensive and less compact than on agar. 



The mycelium is made up of profusely branched, anastimosing, 

 septate, thick-walled hyphse about 2.5 /* in diameter. (See PL III, 

 fig. 9.) 



The fungus does not fruit freely on culture media, and so far the 

 writers have been able to secure spore-bearing pycnidia only on ster- 

 ilized apple wood and corn-meal agar. Pycnidia-like bodies are 

 formed in great abundance on all media, but these arc for the most 

 part sterile. In apple-wood cultures the fungus generally fruits well, 

 producing little groups of pycnidia rich in spores. 



144 



