POTATO IMPROVEMENT 221 



colony to England, including Thomas Herriott. Probably pota- 

 toes were part of the stores obtained in the West Indies by Drake 

 and these Herriott introduced into Ireland about 1586. This was 

 the second introduction into Europe, the Spaniards deserving 

 the credit for the first introduction. It is not known from what 

 source the English colonists of Virginia and Carolina first obtained 

 the potato, but it is generally believed to have been from Spanish 

 or other travelers. Gerard described and illustrated the potato 

 in his "Herbal" in 1597. The variety he described possessed 

 light brown to yellowish tubers and violet to almost white 

 flowers. 



Inheritance. 1 The transmission of potato characters through 

 the seed is in conformity with Mendelian principles. Vegetative 

 propagation allows the breeder to perpetuate any desirable geno- 

 type even though heterozygous, which is the usual condition in 

 the potato plant. While, in general, self-fertilization of a com- 

 mercial variety gives rise to seedlings which vary a great deal, 

 it is comparatively easy to obtain homozygosity for some 

 characters. 



Tuber shape and size are important characters which are used 

 as one means of varietal classification. Tuber shape has been 

 found to depend essentially on the presence or absence of a single 

 factor for length. According to this hypothesis a tuber may be 

 homozygous long, homozygous round, or heterozygous long. 

 Heterozygous long is the most variable of the three conditions. 

 In one experiment two varieties with round tubers when selfed 

 produced nothing but round tubers, while twelve varieties with 

 oval tubers, when selfed, produced long, oval, and round tubered 

 progeny. Nilsson (1912-13) found one variety of potato that did 

 not breed true for round tubers. Long tubers were dominant to 

 round in Fruwirth's (1912) experiments. 



Depth of eye is a character of considerable economic impor- 

 tance. In general, shallow eyes were found to be dominant over 

 deep eyes. 



Several factors, in addition to a chromogen body, have been 

 recognized in tuber coloration. Red potatoes contain two genes, 

 R, a reddening factor, and D, a developer of pigment. Purple 

 and black tubers have, in addition to R and D, another factor, 



1 The following discussion is based on inheritance studies made by 

 SALAMAN (1909-11, 1910-11, 1911, 1912-13) and EAST (19106) except 

 where otherwise noted. 



