COMPOSITION AND CHARACTEE, AND ROT RESISTANCE. 27 



vigor or inherent disease resistance of the plant itself. Seed dealers 

 in this coiuitry, as well as in England, have also expressed a prefer- 

 ence for seed from a crop that has not been very highly fertilized, 

 especially with nitrogenous manures. The most detailed study along 

 this line is that of Laurent,'* whose results indicate that nitrogenous 

 fertilizers predispose both the foliage and the tubers of the plants to 

 the attacks of Phytophthora. This is in harmony with the general 

 opinion of practical potato growers, that high manuring increases the 

 liability to disease. 



COMPOSITION AND CHARACTER OF TUBERS AS RELATED TO ROT 



RESISTANCE. 



There is considerable evidence that the chemical composition of the 

 tubers bears a direct relation to resistance to rot. Paulsen ^ claimed 

 that varieties rich in nitrogen compounds are less resistant to disease 

 than those rich in starch. He classed most of the early varieties in 

 the first category and found the larger percentage of the second class 

 to be of the late varieties. The table varieties of better quality were 

 also of the first category. 



Petermann'' has recentl}^ made field and laboratory studies at the 

 Belgium Experiment Station. These led him to practically the same 

 conclusions, viz, (1) that varieties richer in amids are more liable to 

 rot, although of superior table quality; and (3) that varieties relatively 

 richer in starch, including several recently originated German factory 

 varieties, are less liable to rot but are of inferior quality for table use. 



Sorauer'' has published similar conclusions, and he made more 

 detailed statements as to his belief on this point in conversation last 

 summer. In general, he believes that the varieties richer in protein 

 are more liable to disease, while those richer in starch are more 

 resistant. This probably explains his observation that the yellow- 

 fleshed varieties, which are in higher repute in Germany for table use, 

 are more liable to disease*^ than the white-fleshed varieties which are 

 grown for factory purposes. His further observations in harmony 

 with this idea are that the thicker and rougher skinned red varieties^ — 

 e. g., Dabersche — have a higher degree of disease resistance, coupled 

 with relatively high starch and low protein content, whereas the thin- 

 skinned white varieties, which are more liable to the disease, have 



'^f Laurent, Recherches exp. sur la mal. des plantes, Ann. Inst. Past., XIII, pp. 

 1-48 (1899). 



''Biedermann's Centralbl. Agr. Chem., 1887, p. 107. 



^Bul. Inst. Chim. et Baot. Gembloux, 70 (1901). 



^'Jahresher. d. Sondersaussch. f. Pflanzensch., XII and XIII (1902 and 1903). 



^See evidence of this also in Jahresber. d. Sondersaussch. f. Pflanzensch., XIII, 

 1903. 



/Bee also statement that red varieties are in general more resistant; Jahresber. d. 

 Sondersaussch. f. Pflanzensch., XII, 1902. 



