84 The Potato 



oval and elongated. The kidney and cylindrical shaped tubers have 

 about the same length of axis, but seem to have different factors de- 

 termining diameter. 



Depth of eyes. — The deep eye is a recessive character and breeds 

 true. Shallow eyes are dominant over deep eyes, but often not com- 

 pletely so. 



Sterility. — Salaman ^ finds that a tendency toward sterility is 

 dominant over a fertile condition of the pollen. In a cross of Record 

 (no pollen) X Flourball (abundant pollen), the Fi generation gave 

 12 pollen-bearing plants and 20 with no pollen. One of the sterile 

 (for pollen) Fi plants crossed with the male parent used above gave 

 19 pollen bearing to 20 non-pollen bearing. This is practically the 

 1 : 1 ratio which we should expect to get from a cross between a 

 heterozygous and a pure recessive. 



Stolon length. — The stolons on which the tubers are borne are un- 

 usually long in the species, S. Commersonii and S. verrucosum, often 

 reaching 6 feet or rnore. In the domestic varieties the stolons 

 average 9-12 inches. Very long and very short stolons breed true. 

 Intermediate stolons break up into various lengths, suggesting the 

 action of multiple factors. Salaman ^ thinks there may be two or 

 perhaps three pairs of factors involved. 



Plant habit. — Salaman ' states that upright and prone habit of 

 plant are due to the action of one pair of factors. A duplex condi- 

 tion of the factor for uprightness gives a perfectly upright plant. 

 Heterozygotes, Aa, are upright at first, but droop toward the close 

 of the season. Prone plants have the constitution aa. Both prone 

 and upright plants bred true to type. Intermediates gave a ratio 

 of 1 upright : 2 intermediates : 1 prone, when selfed. 



Shape of berry. — The seed berries of domestic varieties of pota- 

 toes are round. Those of the wild species tend to be long. Salaman 

 concludes that one pair of factors is involved. He believes the long 

 berries to be due to a duplex dose of a factor for length. When the 

 length factor is simplex, a heart-shaped berry results. The double 

 recessive factor gives round berries which breed true to shape. 



' Salaman, R. N. A Lecture on the Hereditary Characters of the 

 Potato. Roy. Soc. Hort. Journ., 38 : 34-39 (1912-13). 



