BIvACKI^EG. 315 



cultural crop. Here infection either came with the seed or 

 existed on land never before under the plow, which latter seems 

 improbable. 



A field of four acres on the University Farm in 1907 was 

 planted with seed from 5 or 6 different sources. Along one 

 side 3 barrels of selected potatoes, Green Mountain variety 

 each from a different source were planted. The plants from 

 one of these barrel lots showed quite a percentage of black- 

 leg but careful search, several times on dift'erent dates, over the 

 remainder of the field failed to reveal a single diseased plant. 

 The disease had not been previously seen on this farm. Case 

 after case has been seen on different farms where one field or 

 part of a field developed the disease while another field on the 

 same farm or a part of the same field did not show it. Inquiry 

 has invariably resulted in showing that the seed tubers from the 

 two dift'erent areas came from different sources. Several 

 attempts have been made to trace the seed to see if the disease 

 was present on the farm where its was produced. A few cases 

 presented data of some reliability, giving an affirmative answer 

 to the question. The too common practice of growers sell- 

 ing their entire crop in the fall or winter and then picking up 

 seed from mixed lots of local dealers, makes it impossible in 

 most cases to trace the source of the seed. 



In describing the outbreak on the Station farm in Vermont, 

 Jones makes the following significant statement : — "The field 

 was planted with Green Mountain potatoes, the seed being from 

 Houlton, Maine."* This statement is all the more significant 

 in view of the fact that as a specialist in the study of potato 

 diseases he has conducted experimental work on this farm for 

 twenty years, has had an intimate knowledge of the condition 

 of every crop of potatoes raised thereon during this time, and 

 this was the first recorded outbreak of blackleg. 



IVofessor T. C. Johnson of the Virginia Truck Experiment 

 Station says:** "I examined a field in Augusta County, (Vir- 

 ginia) in which some Maine grown Cobbler seed was planted, 

 and also some home grown seed of other varieties. In portions 

 of the Cobbler field the injury from 'l)lackleg' was as much as 



* 1. c, p. 258. 



** In correspondence, September 1909. 



