230 University of California Puhlications in Botany [Vol.5 



The F^, populations in some cases show a remarkable increase in 

 the range of variability as compared with the parents and F^ hybrids. 

 This range in no case is equal to the total combined range over which 

 the varialiility of both parents extend. Thus in some cases the means 

 of individual F. plants may be as small as or smaller than the mean 

 of the smallest-flowered parent plant, but in no case, for the same 

 Fo distribution, is the mean flower-size of the largest-flowered Fg 

 plant as great as the mean of the largest-flowered parent individual. 

 Indeed, in only one case do Fo individuals approach the size of the 

 largest-flowered parent plants and at the same time show individuals 

 with means within the small-flowered parental range. As has above 

 been noted, a certain proportion of this increase in variability in Fo 

 populations may be ascribed to the active interference of various 

 external and internal factors attending development. It is signifi- 

 cant, in this connection, that the flower-size of the F. hybrids shows 

 in the greater number of cases an increase of variability 'toward the 

 smaller end of the parental range. 



Though a number of F3 families were groA\Ti, it was not foimd 

 possible to measure flow^ers on more than one group of plants. The 

 mean flower-size, for spread of flowers, of the F^, plant from w^hich this 

 F., population was derived was 24.89 mm., while the mean corolla 

 spread of the 51 F.. plants was 27.43 mm. The range of this F. 

 population for spread of flowers was not as great as the range of the 

 17 Fo plants of the previous year, though it is approximately the same 

 so far as the limits of the range are concerned. The mean — 27.43 mm. 

 — is approximately the same as the 1913 F^ mean of 27.59 mm. It is 

 entirely possible that of many other F.. families some might have 

 shown significant differentiation but the relatively few measurements 

 made upon three other F., families showed in general a range corre- 

 sponding to that of the one F.,, the distribution of which is given in 

 table 1. The range of this F;. with reference to length of corolla tube 

 shows an extraordinary extent, yet the mean is approximately the 

 same as the mean between the parents. 



Transmitted February 11, 1915. 



