No. 661] GENETIC AL STUDIES ON JENOTHEBA 



559 



"mutations." The process of segregation, of course, 

 adds or subtracts nothing from the sum total of the fac- 

 tors but merely distributes them variously to the gametes 

 that are formed. The increase or loss of factors in the 

 offspring of a hybrid results from the mating of gametes 

 which carry a greater or less number of factors. 



Mendelism in its extreme expression may then be said 

 to rest in large part on a law of the conservation of fac- 

 tors. This means that factors could never disappear 

 from a genetic line of development if all of the gametes 

 were mated and if all of the zygotes matured. It fol- 

 lows that the factors contained in an F, hybrid must all 

 come out in an F 2 generation if that generation is suffi- 

 ciently numerous. 



The most striking specific problems brought forward 

 by the data presented in this paper are: 



1. The explanation of the large groups of dwarfs 

 thrown off in the F 2 generations and repeated by certain 

 plants in the F 8 . 



2. The explanation of the well-defined progressive evo- 

 lution, excluding the dwarfs, exhibited by these same cul- 



With respect to the dwarfs the ratio of their produc- 

 tion in the most striking of the Fo generations is as 

 follows: 



The Fj hybrid 10.30La gave 141 dwarfs in a culture of 

 1,451 plants (ratio about 1:9). 



The F, hybrid 10.30LZ> gave 147 dwarfs in a culture of 

 992 plants (ratio about 1 : 5.7). 



These are large ratios, considerably above the 1:15 

 which might be expected if the range of size depended 

 upon so simple a matter as the presence or absence 

 two factors. It must be remembered that the dw» 

 were very much smaller than either parent, as best sh- 

 in the dwarfs from the plant 10.30L& (Fig. 5), wh 



