28 DISEASE KESISTANCE OF POTATOES. 



proportionately less starch and more protein. As a rough empirical 

 test he considers that if, when a fresh tuber is cut open, the flesh 

 browns quickly on exposure to the air and the vascular bundles darken 

 soon, it is evidence of hig-h protein content, and therefore of liability 

 to disease, whereas the reverse condition is evidence of probable dis- 

 ease resistance. Professor Sorauer also emphasized to the writer his 

 belief in the relation of soil, manuring-, or other cultural condition to 

 disease resistance. The testimon}^ secured elsewhere in Germany, as 

 well as from American sources, is in harmon}^ with these ideas so far 

 as it goes. 



While character of skin is probably a less relial)le index to rot 

 resistance than is chemical composition, yet the writer has learned of 

 several potato experts in America, as well as others in Europe, who 

 regard the red varieties, especially such as have a rough skin, as less 

 liable to rot than are the white thin-skinned varieties. The Dakota 

 Red has often been cited as an example of this class in America. 

 Abundant evidence can be found, however, especially from English 

 experience, of high disease resistance coupled with a thin, white skin. 

 Breeders aiming at disease resistance need not turn from the white- 

 skinned varieties. 



CHARACTER OF STEM AND FOLIAGE AS RELATED TO DISEASE RESISTANCE. 



In connection with the question of the relation of the character .of 

 the stem and foliage to disease resistance it is not safe to go far in 

 generalizing. Mr. Lasham, potato expert and breeder with Sutton & 

 Sons, considers that a stem that is strong, rough, and hard, almost 

 woody at the base, is an important character if the plant is to be most 

 highly disease resistant. The nature of the foliage is considered by 

 others to be of greater importance, the preference being for small 

 leaflets, rough and relatively thick rather than large and flabby. A 

 rich dark- green is preferred to the lighter colored foliage. It seems 

 inherentl}' probable that the character and color of foliage should 

 stand in close relation to the other matters which have with more cer- 

 tainty been shown to be related to disease resistance, viz, general 

 vigor and capacity for starch manufacture. Those giving further 

 attention to disease resistance may, therefore, well bear these sugges- 

 tions in mind. 



DISEASE-RESISTANT VARIETIES OF EUROPE. 



When all the factors are considered, two important things become 

 evident: First, that no variety will maintain its disease-resistant qual- 

 ities indetinitely, losing them sooner in one locality than in another; 

 second, that no one variety will be equally disease resistant in all 

 countries, i. e., what is best suited to one may not be to another. 



