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 were 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 ercp. 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. 
