78 MASS. EXPERIMENT STATION BULLETIN 185. 



dark mottled, three light mottled, three self-colored, and four white, which 

 is in harmony with the results shown in the table. No dark mottled beans 

 could breed true, and no extracted light mottled beans could jdeld self- 

 colored offspring. 



In cross 230 Golden Carmine, which must be, according to the fore- 

 going hypothesis, of the constitution PYZo, when crossed with White 

 Marrow yields no dark mottled beans, but does yield self-colored beans. 

 White Marrow must therefore be pyZo, and the proportion in F2 one of 

 9:3:4. The self-colored beans in F3 and F4 are from the heterozygote 

 parents, and are not, like the other light mottled beans, extracted from the 

 heterozygote. In cross 309a no self-colored beans are produced. Red 

 Valentine must, from its appearance, be PYZO, and Wliite Marrow must 

 be pYZo, The theoretical F2 proportion — 9 dark mottled, 3 hght mot- 

 tled and 4 white — is closely approximated. In cross 366 Burpee Kidney 

 is like Red Valentine and Wliite Marrow pyZo as in cross 230, the non- 

 appearance of light mottled beans in F2 being due to small numbers. In 

 cross 327 Wardwell, a bean with a dark mottled eye, when crossed with 

 White Marrow yields no light mottled beans, while in 327a light mottled 

 beans appear, but no self-colored ones. This can be explained on the 

 assumption that in cross 327 the White Marrow plant used was of the pyZo 

 strain, while in 327a a plant of the constitution pYZo was used. 



In cross 141, Davis Wax X Keeney Rustless, no self-colored beans are 

 produced, and as in all other crosses of Davis Wax it has the formula 

 pYZo, while Keeney is PYZO. 



In crosses 67 and 68 Burpee Stringless must be PyZO and White Mar- 

 row pYZo. On the assumption that the O and Z factors are associated or 

 coupled, the failure of light mottled progeny to appear in the proportion 

 18:0:6:9 must be due to the small numbers involved, and this lot belong 

 properly on the second hne above, it being of the same constitution as 

 the F2 heterozygote. Similar cases are found in crosses 181 and 73. The 

 appearance of a single self-colored plant from a light mottled parent in 

 cross 68 is unexplained unless it be a stray plant. Such a plant undoubtedly 

 did appear in a lot all of which were supposed to be from a light mottled 

 parent plant. It is not thought that these seeming irregularities are suf- 

 ficient to throw serious doubt upon the general theory of the inheritance 

 of types of mottling, but they are recorded in order to fully present the 

 facts as they have appeared. 



Besides the tj-pes of motthng here discussed a wholly different type has 

 been encountered in certain crosses involving White Marrow. This is a 

 fine marbling or cloudy mottling, bluish, brownish or bluish black in color. 

 It is similar to that shown by the variety Cut Short. Data bearing on this 

 are limited. In a cross of Prolific Black Wax X White Marrow this type 

 of mottling appeared, sometimes covering the whole bean and sometimes 

 confined to a limited area, giving an eyed bean. Three plants with this 

 type of mottling yield the parent type and white in the numbers of 6:9, 

 20:4 and 5:1, respectively. They have been extracted from both self- 

 colored and dark mottled parents. 



