Forms Having an Extra Chromosome. 



25 



TABLB I. 

 Mutations in CEnothera with an extra chromosome. 



ABBCDEFG, fertilizes one which is ABCDEFG. Such gametes 



AA 

 could arise from an meiotic separation in lata in the first 



case, and an separation in the second case, the ABB and 



AB groups (disregarding the other chromosomes) then uniting in 

 fertilisation to form a nucleus with 2 A's and an extra B, although 

 derived from a plant in which there were two B's and three A's. 

 The chances of this happening are small, especially when we 

 remember that lata produces practically no functional pollen 

 grains, and that these nearly all have 7 chromosomes. Nevertheless 

 it is not impossible. 



In lata x lamarckiana the chances of getting a mutant with a 

 new extra chromosome are greater than in lata selfed, for we may 

 suppose (1) that a 7-egg, i.e., ABCDEFG, is fertilised by a sperm 

 having two members of some other pair than A, the latter condition 

 having arisen through an irregular separation involving the non- 



