124 SEVENTEENTH REPORT. 



He repeated this a .second aud a third veai- with similar results, 

 specimens from this man's field have been examined and were 

 typical Curly Dwarf material. There is little doubt but the ex- 

 periments iMjrformed were with Curly Dwarf. 



Last year I visited the field of a farmer who had followed con- 

 *sistently the practice of using his small potatoes for seed-stock. 

 In this field instead of an occasional Curly Dwarf plant, there 

 were at least 10 per cent of the hills Avith plants which produced 

 onlv a mat of stunted Avirv yrowtii, and wiliose vield was a dozen or 

 juore small worthless tubers. It is signifirant that many of these 

 tubers Avere of a size such that they would be planted if the practice 

 •of planting small potatoes were followed. It is further significant 

 that the disease was not found in fields where high grade seed had 

 been introduced. \Vith seed of ordinary size from a prolific stock, 

 and especially if the stock be a pure line, this disease should be 

 •entirely unknown. So far the disease has been noted in Kent, 

 Montcalm aud Van Buren counties. 



The Leaf Boll Disease. Leaf roll Avas found for the first time in 

 Michigan in 1911: although it has doubtless been present for some 

 time in some varieties. In Jul}', 1914, a fcAv roAvs of a trial lot 

 of potatoes, Twentieth Century, obtained along with a AA'hole assort- 

 ment of varieties and strains of potatoes for testing on the College 

 grounds, shoAved curled foliage in more than 90 per cent of the 

 plants. These roAvs presented a marked contrast to the other rows 

 whose leaves Avere normal. The juice of these plants gave a marked 

 reaction Avith gum guaiac, turning it blue instantly. Other varie- 

 ties gaA'e but a faint reaction after an hour. In August, Dr. Otto 

 Appel Avho AAas Avith the party of scientists, examined the plants 

 and pronounced the disease typical Leaf Koll. Leaf Roll is uoav 

 known from seA'eral counties, St. Clair, (in imi>orted seed) Oak- 

 land, Ingham, and Allegan County. 



T^af Koll (PL VIIA) and Curly DAvarf are diseases of the type 

 called ''Physiological" for Avhich no parasite is knoAvn, They cause 

 the type of disorder significantly called "running out of seed,'' 

 There is ahvays danger from disea.ses of this tyjie and especial 

 effort has been made to examine fields of gi'OAvers anxious to de- 

 A'elop good, safe, seed-stock, and to certify these as free from a 

 dangerous per cent of such diseases. For a full discussion of these 

 diseases the comprehensive bulletin by Orton* may be cited. 



'Orton, W. A., U. S. Dept. Agr. Bui. 04: 4Spp. IG pis. (1914). 



