82 



of the seed, that if possible all types and grades of seed should be 

 germinated, and that seedlings showing all degrees of vigor should 

 be grown to maturity, since variation in seed size, etc., is a direct 

 suggestion of the possible segregation of the original characters. 



A second part of the report treats of the "quantitative expres- 

 sion of imperfect dominance in the corolla diameters of the flowers 

 on the hybrids produced from three varieties of Nicotiana acumi- 

 nata.'' These three varieties differ only in regard to the diam- 

 eter of the open corolla, a feature which is practically constant 

 for each variety giving an average for the varieties of 13 mm., 

 20 mm. and 27 mm. with fluctuations never greater than 2 mm. 

 more or less than the mean for any one variety. 



Measurements were made of the corollas on five groups of 

 hybrids between these varieties. In every group the average 

 of the measurements was intermediate between the average 

 corolla diameters of the respective parents. The fluctuations, 

 however, in the Fi plants of all the hybrid groups taken together 

 was from 13 mm. to 30 mm. or as great as the extremes exhibited 

 by the parents. The fluctuation, however, within a single group 

 was almost twice as great as the greatest fluctuation in any of 

 the parental varieties. 



In a later paper Dr. Goodspeed gives a preliminary report on 

 the F2 hybrids of these same forms grown during the summer of 

 1912. In these still greater fluctuation appeared. For example, 

 of the F2 plants of the cross "III9 XUcT" (small flowered 

 variety X variety with corollas of intermediate size) every one 

 bore "flowers smaller than the smallest ever measured on the 

 small-flowered parental variety III, and every plant also bears 

 flowers larger, with possibly one exception, than the largest 

 flowers measured, on variety II in 1900 and 191 1." The data 

 thus exhibit cases of hybridization which produce in the Fi and 

 F2 generation greater degree of fluctuation than was seen in the 

 parents. 



The author states that "a sample monohybrid ratio was antici- 

 pated for the results of the measurements of corolla diameter of 

 flowers on F2 individuals," but that the results do not admit of 

 any handy or helpful interpretation by the Mendelian notation. 



