2l6 R. RUGGLES GATES. 



(RrR'r'). On the other hand, if the chemical transformation 

 of a fresh chromosome takes place in a homozygous monomeric 

 plant (RR), then the dimerous individual derived from such a 

 monomerous plant should have the constitution RRR'r'.^ It 

 would be possible to determine between these two alternatives 

 by breeding tests. If the constitution of the plant is RrR'r' its 

 offspring should give a 15:1 ratio. If it is RRR'r' they would 

 all be red in Fi and F2. But plants having the former formula 

 could also be produced by the mismating of chromosome-pairs 

 during meiosis in RR plants. 



If we now return to the table (p. 210) and examine the F2 from 

 the reciprocal cross (rubricalyx X grandiflora) we find a total 

 absence of 15:1 ratios, showing that not only was the rubricalyx 

 parent of this cross monomerous but its offspring remained so. 

 The parent of this cross was a member (No. IV., 8) of the monom- 

 erous family 33:11. As will be seen from the table, two of the 

 F2 families from rubricalyx X grandiflora gave perfect or almost 

 perfect 3:1 ratios. Four others gave 5:1 ratios, three of which 

 were perfect and the other very close to expectation as already 

 pointed out. I have at present no further explanation of these 

 5:1 ratios to offer, but it seems probable that their significance 

 will later become apparent. 



Ratios more or less in excess of 3:1 could be obtained from 

 plants homozygous for one factor, if there was a tendency for 

 mismating of the chromosomes in meiosis. But this will not 

 account for the definiteness of the 5:1 ratios obtained. 



Turning to the F3 of grandiflora X rubricalyx the full data are 

 given in my book (p. 255). Four families were constant for 

 R, 3 constant for r, 2 families numbering respectively 283 and 20 

 plants bred true to an intermediate condition, and 2 families 

 split in the ratio 4:1, as shown in the table (p. 211). The excess 

 of R's in the last two families is a significant excess over 3:1, 

 however it is brought about. 



In the F3 of rubricalyx X grandiflora, four families give ratios 

 nearest 2:1, one family near 3:1, one near 5 :i and four very close 

 to 15:1. Whatever the significance of the 2;i and 5:1 ratios in 



1 We have already found it highly improbable that a plant Rr could be directly 

 transformed chemically into RrR'r', since we should anticipate that the chromo- 

 some r would undergo a mutation before the chromosome r'. 



