Studies of Teratological Phenomena. 127 



interpretation of the variableness in dominance shown in the plants of 

 the different Fi families. It is not improbable that the F2 progeny 

 of some of these species crosses, if they were obtainable, would represent 

 plants of the constitution AA, which would promote or allow a very 

 much greater abnormal expression that that of the standard Xi race 

 (300 — 309). Theoretically, I should expect such segregates. 



17. It is of interest to note the somatic effect when the factor A 

 is present in simplex condition. Instead of a progressive increase in 

 expression, as the plant approaches maturity, the factor seems to be 

 unable to maintain its normal (under Xi) rate of development after the 

 first one, two, or three floral whorls are laid down in morphogenesis. 

 As a consequence, the gynoecium does not usually show the most 

 abnormal expression of the factor A in the eight or nine different Fi 

 combinations grown. In 303 — 1 — 13X327, the greatest alteration 

 occurs in the corolla, the least in the csdyx and the next to the least, 

 in the gynoecium. Practically the same relationsliip between the different 

 floral whorls and the somatic expression of A, is apparent in all the 

 other Fl hybrid families represented in Table 13. The exceptions to 

 this generalization are 324 X 301, 304 X 402 and 301 X 396. The first 

 combination does not follow the floral organs (see materials). The 

 second case, 304 X 402, is explained on the grounds of relationship, 

 the geue complex in both races being extremely favorable to the normal 

 expression of A. 301 X 396 shows only a slight deviation from the 

 general rule and is possibly due to error resulting from the manner in 

 which the data from it were collected. 



18. The origin of factor A could be pictured as either a loss or 

 a gain in actual protoplasmic substance. It was either a sudden dropping 

 out of something essential to normal development (402) or it may have 

 been an abrupt change in the germ -plasm. As Morgan and others 

 before him have suggested, changes in chemical configuration (isomerism) 

 of protoplasm may account for the origin of new factors and such a 

 conception is preferable to the idea of an actual protoplasmic loss. The 

 Nicotiana factor A is both discontinuous in origin and in inheritance. 

 Whatever be its germinal nature, it arose as a unit and is trans- 

 mitted intact. 



19. Calycantheray (B) in crosses is transmitted as a single unit 

 factor, giving in the progeny of an Fi Bb plant, segregates in the 

 proportions of 1 BB : 2 Bb : 1 bb. When the calycanthemous and 

 fasciated races are crossed, the resulting AaBb individuals show only 



