36 THE BITTER EOT OF APPLES. 



Summing up the evidence now at hand as to the causal relationship 

 between the bitter-rot fungus (Glomerella rufomaeuJans) and the 

 apple cankers found in certain apple orchards in Illinois and other 

 States, we find (1) that conidial spores of this fungus which will pro- 

 duce the bitter rot in apples occur with great regularity in the cankers; 

 (2) that such conidial spores taken either directly from diseased apples 

 or from pure cultures made from cankers or diseased apples, when 

 inoculated into the living bark of growing apple-tree branches, will 

 produce apple cankers resembling those found in the orchards; (3) that 

 conidial spores and asci and ascospores are contained in such artificially 

 produced cankers, which, when inoculated into apples, produce the 

 bitter rot. 



Taken together, these facts seem to prove beyond question that the 

 bitter-rot fungus can grow in apple branches, that by so doing it 

 forms cankers, and that after a time spores are formed in such cankers, 

 which produce the bitter rot in apples. 



Although this fact seems established at present, the writers are by 

 no means convinced that sufficient proof is yet at hand which would 

 warrant the statement that all of the cankers found in the Illinois 

 orchards were formed by the bitter -rot fungus. The resemblance 

 between the canker formed by the black-rot fungus Sphaeropsis malo- 

 rum Peck on apple limbs in New York (Paddock. 1899 and 1900) and 

 the cankers formed in Illinois suggested at first that the latter were 

 formed by the black-rot fungus. This supposition was strengthened 

 by the almost constant presence of spores of Splixropx't* malorum 

 Peck in the Illinois cankers. The black-rot fungus is known to form 

 cankers on apple limbs with great readiness, and the black rot is a 

 common enemy of the apple in Illinois and adjacent States. The 

 writers are therefore of the opinion that it is not at all improbable 

 that the Illinois cankers are formed in part by Sphaeropsis malorum 

 Peck. The bitter-rot fungus may get into the young Sphaeropsis 

 cankers and both fungi may grow side by side. Considerable addi- 

 tional work will have to be done with these cankers before their exact 

 identity will have been established. 



SPREAD OF THE BITTER ROT. 



Nearly all those Avho have studied the bitter rot agree that the fungus 

 is very erratic in its time of appearance. The disease may be prevalent 

 year after year in a particular part of an orchard without occurring in 

 other places in the same orchard or in other orchards in the immediate 

 locality. It has been repeatedly noted that the rot seemed to start 

 in one tree or a group of trees close together and that it spread from 

 the center to adjoining trees. 



Observation showed that the rot was more likely to appear on trees 

 which had once had the disease than on trees previously free from it. 



