320 Varietäten, Descendenz, Hybriden. 



11. From the light seed 18 per cent of „dominants", 33 per cent 

 of „recessives" and 49 per cent of „blends" and „intermediates" 

 could be recognized. 



12. The seed produced by close fertilizing one plant ofA\ Taha- 

 cum var. macrophylla, which was harvested in 1907, showed under 

 a readinglens a much greater degree of uniformity in shape and 

 size than did the F^ hybrid seed similarly examined. The same was 

 true for the seed of N. Tabacum var. virginica similarly produced 

 on two successive years — 1906 and 1907. 



13. The average weight of 100 virginica seeds of 1906 was 

 0,0001 grams less than the average weight of 100 virginica seeds 

 of 1907. 



14. The average weight of 100 virginica seeds of 1906 or 1907 

 was 0,009 grams less than the average weight of 100 macrophylla 

 seeds of 1907. 



IL Quantative expression of imperfect dominance in the corolla 

 diameters of the flowers on the hybrids produced from three va- 

 rieties of Nicotiana aciiminata (Grab.) Hook. 



Summary of results: 



1. The experimental material consisted of three varieties of 

 Nicotiana aciiminata. The three varieties are distinguished from one 

 another almost solely in the diameter of the limb of the salverform 

 corolla of the flowers. 



2. The differences in corolla diameter among the three varieties 

 were practically constant throughout two seasons during which the 

 corolla diameters were measured in the Botanical Gardens of the 

 University of California. The three diameters were 13 mm., 20 

 mm., and 27 mm., with fluctuations never exceeding 2 mm., either 

 greater or smaller than the mean diameter in each case. The three 

 mean diameters and the fluctuation noted were obtained on the 

 basis of approximately 800 measurements of flowers of the three 

 varieties. 



3. From six successful cross-poUinations - the three crosses 

 between the three varieties and the reciprocal crosses — five groups 

 of hybrid plants were brought to maturity (100 plants at the ope- 

 ning of the season, and 65 at the close). Approximately 2750 mea- 

 surements of the corolla diameters of flowers on hybrid plants 

 were made. 



4. The measurements of the corolla diameters of the flowers on 

 the plants of each group of hybrids gave an average diameter for 

 each group which was practically the same as the calculated 

 average between the corolla diameters of the corresponding two 

 parents. In other words, each of the five average hybrid corolla 

 diameters formed intermediates in size between the corolla diame- 

 ters of the parents of the corresponding cross. Each cross and its 

 reciprocal gave practically the same result in this connection. 



5. Variety II, called an .,intermediate", in reference to corolla 

 diameter, is truly an intermediate between the large and small 

 flowered variety of N. aciiminata. This is shown by the fact that 

 when the large and small varieties are crossed the average corolla 

 diameter of the hybrid flowers approximates fairly closely the ave- 

 rage corolla diameter of this „intermediate" variety. 



6. Among the corolla diameters of the flowers of all the hybrid 

 plants a wide ränge of fluctuation was observed. This fluctuation 

 included diameters from 13 mm. to 30 mm. 



7. The fluctuation 13 mm. to 30 mm. is as great as the diffe- 



