144 University of California Puhlications in Botany [^ol. 5 



VI. SUMMARY OF RESULTS 



The foregoing description of experimental results can be 

 summed up as follows : 



1. The experimental material consisted of three varieties of 

 Xicotiana acuminata. 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 Gar- 

 den 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-pollinations — the three crosses 

 between the three varieties and the reciprocal crosses— five groups 

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

 opening of the season and 65 at the close). Approximately 2750 

 measurements 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 

 diameters of the parents of the corresponding cross. Each cross 

 and its reciprocal gave practically the same result in this con- 

 nection. 



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

 corolla diameter, is truly an intermediate between the large and 

 small flowered varieties of X. acuminata. This is shown by the 

 fact that when the large and small varieties are crossed the 

 average corolla diameter of the hybrid flowers approximates 



