DAIRY AND SEED IMPROVEMENT MEETINGS. 353 



results. Two different types of powdery scab are shown in the 

 next picture. The tuber at the left represents the ordinary type 

 where the tops of the pustules have been rubbed off, leaving the 

 scab-like appearance. The smaller potato at the top shows a 

 decided cankered area where the tissues have been eaten into 

 and hollowed out. So far we have not found this type of disease 

 in the fields of ]Maine. We may expect it in severe cases of 

 soil infection, for the tuber shown in this illustration came from 

 Canada. 



The tubers shown in the next illustration represent a severe 

 type. The slide was made from a photograph of some potatoes 

 which we grew in the greenhouse. 



The next slide shows how, in case of bad attacks of powdery 

 scab, the potatoes tend to wither and show an apparent dry rot. 



RHIZOCTONIA. 



There is a fungus which has long been known to students of 

 pathology as Rhizoctonia. This fungus is, and probably has 

 been for years, as common as pebbles in New England potato 

 soils. Moreover, it is of widespread distribution in the United 

 States. This summer I had an opportunity to examine some 

 hundreds of potato fields in a dozen different states from Maine 

 to California. In very few of these fields did I fail to find the 

 disease caused by this fungus after five or ten minutes' search, 

 and in many instances the injury to the plant was such as to 

 materially reduce the yield on the field. This was particularly 

 the case in one noted potato section of California. In the past 

 a few people have said that the fungus was injurious to potatoes, 

 but as a rule their statements have not been taken seriously. I 

 believe that the work that we have done at our Station during 

 the last fifteen or eighteen months shows conclusively that it 

 may be at times the cause of very serious disease in some parts 

 of Maine. 



As the first picture will show, the ordinary form of this 

 fungus is undoubtedly well known to every housewife or others 

 who have occasion to prepare potatoes for the table. The little 

 brown or black, closely adhering spots of dirt which won't rub 

 off are not dirt at all, but the over-wintering stage of the Rhizoc- 

 tonia fungus, — simply compact masses of the sterile fungous 



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