360 Scientific Proceedings, Royal Dublin Society. 



conditions as regards exposure to infection brought about by the actual 

 lifting of the crop. To attempt to decide between these alternatives, three 

 series of experiments were carried out in the subsequent two years. 



IV. — Field ExrEEiMENTs on the Soueces of Tubeu Infection in 



Canada. 



In an experiment carried out in 1918 the theory that storage rot 

 originates from the contact of tubers with diseased foliage, or with surface 

 soil within five days after it becomes contaminated, was tested in two ways. 

 The stalks, then somewhat blighted, were removed from certain plots and the 

 potatoes were not dug until a period of five days in one case, and eleven days 

 in another, had elapsed. Other plots in which the foliage had been allowed 

 to remain were dug at the same time. The second test devised consisted of 

 digging two series of plots while the leaves were considerably blighted, and 

 immediately treating the potatoes from one series with dilute formaldehyde 

 solution so as to prevent further infection. All the plots were laid out in 

 duplicate. 



It is not necessary to go into the details of this experiment here, since the 

 results were inconclusive for anumber of reasons. The formaldehyde treatment, 

 from which much was hoped, was apparently too drastic ; for serious injury 

 to the tubers, involving complications in decay, resulted. Furthermore, 

 neither interval which was allowed between the removal of the stalks and 

 the digging of the crop (live and eleven days) prevented a large amount of 

 blight rot in storage. If there was anything in soil infection, it seemed as 

 though a longer period must be allowed to elapse to rendei' the crop safe. 

 On the whole, however, the work appeared to be on the right lines. There 

 was least disease in the potatoes treated with formaldehyde, and most in the 

 tubers from those plots which were dug early and while the foliage was still 

 blighted. 



Profiting by this experience, two modified experiments were conducted in 

 1919. These are referred to as experiments A and B. In experiment A the 

 efficacy of leaving a period of six days between the removal of the stalks 

 and the digging of the crop was tested. In experiment B a much longer 

 period was allowed — namely, thirty-four days. One experiment was carried 

 out in quadruplicate and the other in triplicate. The average results are 

 shown in Tables II and III. 



