RELATION OF CANKERS TO BITTER ROT. 35 



maculans). At this time there were no other spores in the canker, 

 such as the brown Splideropsis spores. Inoculations were immedi- 

 ately made with the spores which had formed in the pustules of the 

 cankers produced on the apple limbs, using healthy apples. 



Several days thereafter these apples showed all signs of the bitter 

 rot, and after three days quantities of bitter-rot conidia were produced 

 in the characteristic manner already described. These results proved 

 that the fungus growing in these cankers was actually Glomerella 

 rufomaculans. a Some of the more striking cases of artificial cankers 

 are reproduced on Plate IX. Figures 2, 3, and 4 show artificial can- 

 kers, with control cuts above. Figure 5 shows one of the cankers 

 (fig. I) somewhat enlarged, with numerous black pustules. 



These results showed beyond question that the bitter-rot fungus 

 actually p>roduces the cankers on apple limbs, and is not merely present 

 in cankers which are produced by some other fungus. There was no 

 question as to the purity of the cultures used for inoculating the apple 

 limbs, and as there was no growth in any of the control cuts there is 

 no reason for doubting that the fungus inoculated into the cuts on 

 apple limbs grew in the bark and formed the pustules containing spores, 

 which in turn produced the bitter rot in apples. 



A further proof that the fungus produced the cankers was brought 

 forward by the discovery (by Spaulding, December 24, 1902 s ) of peri- 

 thecia and asci, with ascospores (PI. V, fig. 7) of Glomerella rufomacu- 

 lans, in one of the cankers artificially produced on apple limbs by 

 inoculating conidia of Glaiosporium fructigenum Berk, into apple 

 limbs. Spaulding found that many of the spores in the artificial can- 

 kers were curved very much like the ascospores of Glomerella rufo- 

 maculans obtained in cultures on apple agar. The conidia and asco- 

 spores of this fungus look very much alike — so much so that it is not 

 easy to separate them with any degree of accuracy. The only differ- 

 ence which is at all evident is that the conidia are usually straight, 

 while the ascospores are slightly curved. (PI. V, fig. 6. ) Sections of the 

 canker made by Spaulding showed the presence of perithecia (PI. V, 

 figs. 5 and 7), most of which were empty. Several were found, how- 

 ever, with asci and ascospores. (PI. V, fig. 7.) It seems that the asci 

 in the cankers have as little permanence as do those found in cultures. 

 Clinton refers to the comparatively evanescent character of the asci 

 which he found in the cultures, and we can testify to the same state- 

 ment. So far as could be determined, the perithecia and asci in the 

 cankers were identical with those of Glomerella rufomacidans formed 

 in cultures. Up to this writing no perithecia or asci have been reported 

 from the cankers on apple limbs in the orchard. 



a A preliminary note announcing the proof of a causal relation between the bitter- 

 rot fungus ( Gloeosporiwn fructigenum Berk.) and the apple cankers was published in 

 Science, 16: 699, 1902. 



& See Science, 1 7 : 188, 1903. 



