BIvACKIvEG. 321 



a soft, foul-smelling decay which is apparently of a bacterial 

 nature. While there is every reason to believe that the black- 

 leg organism is capable of causing some of this soft bacterial 

 decay the writer's experience leads him to believe the great 

 majority of it is caused by secondary infection by saprophytic 

 bacteria following the invasion and killing of the healthy tis- 

 sues by the ■ late blight fungus. Attempts to isolate bacteria 

 capable of destroying healthy tubers from those so diseased 

 have invariably resulted in failure. The removal of some of 

 the soft, decayed tissue from such tubers and inserting it in 

 sound tubers led to no decay of the latter, while the same pro- 

 cedure where the decayed tissue was taken from a rotting 

 tuber previously inoculated with the blackleg organism invar- 

 iably produced a characteristic and rapid decay of the healthy 

 tuber into which it was inserted. 



]\Ioreover, this soft-rot of the tuber following and associated 

 with the decay caused by PJiytopJithora hifcstans is familiar 

 to all who have had much practical, field experience with out- 

 breaks of disease caused by this fungus, and has been observed 

 frequently by horticulturists and plant pathologists in this 

 country upon fields which showed no evidence of blackleg 

 upon the growing stems. If the organism was present in suffi- 

 cient degree to cause material loss from, tuber decay it would 

 seem that its appearance on the stem could not have escaped 

 notice. 



Harrison'^ apparently takes an opposite view to the above 

 and seems inclined to attribute to his B. solanisaprus a much 

 more active part in the cause of tuber decay in Canada. He 

 asserts that the Experimentalist of the Ontario Agricultural 

 College and others have confused the terms "blight" and "rot", 

 but fails to state distinctly that Pliytophthora iiifcstaiis not only 

 causes the well known blight of the foilage but also is a well 

 recognized cause of decay of the tuber often referred to as the 

 "late blight rot." He shows, in one instance, at least, where 

 spraying for fungi was practiced, that the real cause of the rot 

 was of a bacterial nature. However, the statements to which 

 he objects such as "The potatoes grown in the Experimental 

 Department have been comparatively free from blight, although 



1. c. pp. 34 and 391. 



