Mar. 24,1923 
Permanence of Variety in the Potato 
959 
than two places. Lot 6, the highest-yielding lot in 1917, gave the 
highest yield in 1918, but in 1919 it was outyielded by lot 2, the lowest- 
yielding lot in 1917. Lot 9, obtained in 1920, gave a yield almost iden¬ 
tical with that of lot 2. Selection practiced by the growers on lots 2 
and 9 had apparently no effect on increasing their productivity. 
(3) The ratio of width to length of tuber was found to be a fairly 
good index by which differences in form could be detected in the Early 
Ohio variety. It furnished a mathematical expression by which the form 
of tubers grown under different conditions and during different seasons 
could be compared. 
(4) The original lots differed in form. The most distinct differences 
were short, oval tubers, short, broad, flat tubers, elongated, cylindrical 
tubers, and distinct modifications of these three forms (see PI. 1, A, B, 
D, C). When grown at University Farm, Duluth, Grand Rapids, and 
Crookston a distinct form which was the same for all lots was obtained 
at each place. At Grand Rapids it was shown that seasonal conditions 
affected the form. At University Farm, sandy loam and clay loam soil 
types produced distinct differences of form. No correlation between 
form and yield was observed. 
(5) Knobs, fissures, prominence of lenticels, depth of eyes, promi¬ 
nence of eyebrows, and color of tubers were characters that were found 
to be unexpressed, expressed, or modified in their expression according 
to the environment under which the tubers developed. The expression 
of these characters on the tuber was not influenced by selection or by 
the environmental conditions surrounding the development of the seed 
stocks. 
(6) Evidence presented shows that potato varieties do not run into 
definite strains, that they are relatively stable under vegetative propa¬ 
gation, and that the method of asexual selection does not offer reasonable 
hope for their further improvement. 
LITERATURE CITED 
(1) Aitken, William. 
1837. THE POTATO RESCUED PROM DISEASE AND RESTORED TO PRISTINE VIGOUR, 
BY A PLAN OP KEEPING AND CULTIVATION POUNDED ON THE NATURAL 
principles op the vegetable economy. Edinburgh and London. 
Original not seen. Review in Quart. Jour. Agr., v. 8, 1837/38, p. 84-96. 
1838. 
(2) Appel, Otto. 
1915. LEAP roll DISEASES OP THE potato. In Phytopathology, v. 5, no. 3, p. 
139-148. 
(3) Cathcart, Earl. 
1884. ON THE CULTIVATED potato. In Jour. Roy. Agr. Soc. England, ser. 2, 
v. 20, p. 266-300, 2 fig. 
(4) East, Edward. 
1908. A STUDY OP THE PACTORS INFLUENCING THE IMPROVEMENT OP THE POTATO. 
Ill. Agr. Exp. Sta. Bui. 127, p. 375-456, 10 fig. Bibliography, p. 
, , 450 - 456 . 
(s)- 
1910. THE TRANSMISSION OP VARIATIONS IN THE POTATO IN ASEXUAL PRODUC¬ 
TION. In Conn. Agr. Exp. Sta. 33d~34th Ann. Rpt., [1909F10, p. 
119-160, 5 pi. Literature cited, p. 140. 
(6) Ehrenberg, Paul. 
1904. der abbau DER karToFFELN. In Landw. Jahrb., Bd. 33, p. 859-915, 
pi. 22-25. Bibliographical footnotes. 
(7) Gtfssow, H. T. 
1918. OBSERVATIONS ON OBSCURE POTATO TROUBLES. I. HETERODERA RADICI- 
cola. In Phytopathology, v. 8, no. 9, p. 491-495, fig. 2-5. 
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