221 



perature they developed a fair growth of the fungus in about six days, 

 and this reached a maximum on about the tenth day. All the tubes of 

 each variety were then assembled and compared with the checks as to 

 their relative amounts of growth. These results were judged by two or 

 three observers independently of each other, and each judgment recorded. 

 For purposes of comparison the relative growth was expressed in per- 

 centages. Although this was a somewhat arbitrary standard its useful- 

 ness is shown by the fact that these independent observations rarely varied 

 more than five to ten per cent. 



For the final results all these tests were made in duplicate and all 

 the observations on any one variety were averaged. These averages may 

 be grouped into three main classes. First, a highly resistant class, those 

 exhibiting a growth of from 1-35 per cent. Second, a middle class, those 

 exhibiting a growth of from 35-66 per cent, and third, a susceptible class, 

 exhibiting a growth of from 65-100 per cent. It was found that those fall- 

 ing into class one \^ere in every case those which were of tested disease- 

 resistance and were practically all of European origin. Those falling into 

 class two were largely of reputed disease-resistance and were also largely 

 of European origin. Those falling into the third class were practically all 

 of American origin and included many of our most important commercial 

 varieties. Since these results, in the main, correspond to those obtained 

 by Professor Stuart, in his field trials, we feel safe in drawing the con- 

 clusion, that thus far our American breeders of potato varieties have been 

 developing types which stand for yield and quality regardless of disease- 

 resistance, while European breeders have been developing disease resistant 

 varieties. This, we believe, explains in a measure, the heavy loss occa- 

 sioned by fungous disease in our American potato crop. Unfortunately 

 the most resistant of the European varieties are not of the best quality 

 and color for the American market. It therefore remains for the potato 

 breeders of this country to develop varieties which combine the desirable 

 qualities of the best American potatoes with the disease-resistant qualities 

 of the hardiest European potatoes. In connection with this it will un- 

 doubtedly be the laboratory method here explained which will be used 

 largely in testing the disease resistant qualities of new hybrids and seed- 

 lings in the attempts to develop this new ideal potato. 



Purdue University, 



Lafayette, Indiana. 



