DISK ASKS OF PLANTS. 1079 



were also carried on upon the resistance of tubers to scab, but the results so far 

 obtained are inconclusive. 



More than 150 varieties of potatoes wore brought together from Europe and this 

 country and planted under identical conditions, some being planted in clay loam 

 and others in sandy loam. Frequent observations were made as to the presence of 

 diseases and the relative amounl of infection. There was some evidence that some 

 of the varieties on the sandy loam were more disposed to the early blight, due to 

 AHemaria solani, than others. The same is true of resistance to tip burn. 



The principal investigations, however, were in connection with the late blight 

 (PhytoptUhora infestans). This disease made its appearance about August K) on 

 Delaware and Green Mountain varieties, spreading slowly, the weather conditions 

 duringAugust not being propitious for its rapid development. The results of the 

 investigations of the foliage are tabulated, from which it appears that a marked dif- 

 ference was to be observed in varieties. The resistance that is claimed for Solamim 

 comrrtersoni to late blight was found to be unwarranted under the conditions of the 

 experiments. 



In connection with the investigations on the resistance to potato rot a careful 

 examination was made of all tubers as soon after digging as possible, and a list of 

 the American varieties showing the greatest resistance to rot on the sandy and the 

 clay loams is given. Keeper, American Wonder, Dakota Red, I >oe Pride, and Late 

 Blightless were the most resistant in both sandy loam and clay loam. The com- 

 parative rot resistance of European and American varieties is discussed, and it was 

 found that on both sandy and clay loam the Dutch, German, and English-Scotch 

 varieties showed much less rot than did the French and American varieties. While 

 disease resistance is important, the commercial standards of this country favor quali- 

 ties in which the German and Dutch varieties are inferior to the American varieties, 

 and at present the writer does not feel warranted in recommending them to Amer- 

 ican growers. 



The relative susceptibility of varieties which form their tubers deep or shallow 

 was investigated, it having been claimed that those forming their tubers near the 

 surface are more subject to rot than others, and while some differences might he 

 noted, yet in both classes of soil about the same proportion of each was affected. 



Potato diseases and their remedies, L. R. Jones and W. J. Morse ( Vermord 

 Sin. l;/,t. 1905,pp. 272-291 ). — In continuation of investigations reported in a previous 

 publication of the station (E. S. R., 17, p. 261) accounts are given of spraying exper- 

 iments, relation of date of digging to development of potato rot, relation of storage 

 conditions to development of rot in potatoes, studies regarding the time and method 

 of tuber infection by the rot fungus, and gaseous disinfection for potato scab. 



The spraying experiments, which were conducted for the prevention of both late 

 blight and rot, were carried on in the field. Bordeaux mixture, consisting of <> lbs. 

 of copper sulphate, 4 lbs. of lime, and 40 gal. of water, with the addition of \ lb. of 

 Paris green, was employed, 2 applications of the mixture being given the plants on 

 August - and 21, respectively. At the expiration of the season the tubers were dug, 

 and the gain at the rate of 161 bu. per acre is attributed to the application of the 

 fungicide. The authors present in tabular form the gains from the use of Bordeaux 

 mixture on late potatoes, covering experiments for the past 15 years in which the 

 average gain for that period is 1 li» bu. per acre due to the treatment. 



In a previous report i E. S. K., 14, p. los4 1 1 he ant hors called attention to the method 

 by which the .-pore- i if the fungus are carried from the leaves to the tubers, and sug- 

 gested spraying the soil with Bordeaux mixture for preventing this infection. The 

 previous trials were repeated in 1905 with good results, ami the investigations show 

 that not only does the disease pass from the leaf to the tuber, but the mam channel 

 is through the soil rather than through the Stem. Spraying experiments for the 

 control of the early blight showed the effect of thorough application of the fungicide, 



