RELATION OF CANKERS TO BITTER ROT. 33 



in other orchards, that a causal relation existed between the canker 

 on apple limbs and the bitter rot, it was by no means positively proved 

 that the bitter-rot fungus (Glomerella rufomaculans (Berk.) Spaulding 

 & von Schrenk) produced the cankers on apple limbs. Experiments 

 were accordingly started to determine whether any such relation 

 existed. Examination of the cankers showed the presence of unicel- 

 lular spores resembling the spores of Glomerella rufomaculans Berk. 

 In most cases there also occurred numerous unicellular brown spores 

 of a fungus which was probably SpTiwropsis malorum Peck. There 

 were spores present now and then of Tricotheciwn roseum and a species 

 of Alternaria, but the unicellular colorless spores ( Glomerella rufo- 

 maculans) and the unicellular brown spores (Sphceropsis malorum) were 

 quite constantly present. The mere presence of spores of any one 

 fungus, even when constantly associated with a canker, is no proof 

 that the fungus producing these spores causes the cankers. It is 

 strong presumptive evidence, but no more. That the colorless one- 

 celled spores were spores of Glomerella rufomaculans was proved after 

 a few days by inoculating some of these spores obtained from a canker 

 into healthy apples. These showed unmistakable signs of the bitter rot 

 in a few days. (See PI. II.) This experiment was repeated man}^ times, 

 using control fruits with every culture. In every case the bitter rot 

 appeared in inoculated fruits, while the check fruits remained sound. 

 Fearing that the spores which caused the disease in these cases might 

 have simply rested in the bark of the cankers, numerous cultures on 

 apple agar were made from pustules in the bark of cankers, and from 

 these pure cultures of the bitter-rot fungus were obtained. 



Spores from such pure cultures were inoculated into sound apples, 

 using control fruits, and these also produced the disease (PI. VI, 

 figs. 3 and 1). These cultures, repeated for several months and under 

 different conditions, left little doubt that the cankers on apple limbs 

 contained spores of the bitter-rot fungus (Glomerella rufomaculans 

 Berk.). 



A number of tests were made to determine whether the spores 

 could be washed from a canker onto apples by water falling on the 

 cankers. The first test of this kind was made by Mr. Simpson. To 

 insure rapid action on the part of the fungus, he punctured an apple, 

 and then allowed water to run from a canker on the fruit. After 

 several days this apple showed unmistakable signs of the disease. 



It now became a matter of considerable importance to determine 

 what connection, if any, existed between the bitter-rot fungus and the 

 cankers. It was very possible that the cankers served merely as 

 lodging places for the bitter-rot fungus or its spores. The presence 

 of numerous spores of what was believed to be Sphceropsis malorum 

 suggested that this fungus, which is known to form cankers on apple 

 limbs (Paddock, 1899 and 1900) resembling those in the Illinois 

 26892— No. 11—03 3 



