548 Length of the Fruit in Oenothera Lamarckiana. 



The mean fruit-lengths for these six seed-parents were 

 15.6,, 17.0, 18.2, 19.2, 20.2 and 21.4; the average of 

 which is 18.6 mm. 



The fruit-length of the seed-parent chosen in 1891 

 was 20.6; from which we see that the above figures are 

 nothing more than fluctuations round a similar mean. 



The harvest was again treated in the same way ; the 

 mean fruit-length was determined for each plant from the 

 total length of the lowest five good fruits : in the table 

 on page 547 are given the numbers of individuals ex- 

 hibiting the various lengths written in the column to 

 the left. 



Here are the values calculated from this table ; to- 

 gether with those of their ancestors and of the seed- 

 parents {S) chosen each year. 



These figures show that the mean fruit-length de- 

 creased about as much, as a result of thrice repeated 

 selection, as they had increased in 1892 as the result of 

 the heavy manuring of 1891. Regression took place, as 

 was to be expected, in the two years covered by the ex- 

 periment. The amplitude of variation exhibited a marked 

 increase in this experiment; the external and internal 

 causes affecting the growth of a plant are obviously 

 multiplied by the choice of ill-favored individuals under 

 favorable conditions of cultivation. In other words : 

 selection and cultivation exert their influence in opposite 

 directions in this case, whereas in the long-fruited race 

 they exerted it in the same direction; hence the ampli- 



