18 



INHERITANCE IN CANARIES. 



whether this ticking is an accident that may be eliminated by further 

 dilution with yellow blood or darkening with "green" blood or whether 

 it is a unit-character like mottling which persists, defying all attempts 

 at dilution. The history of some matings to test this point is given in 

 table 6, in detail. 



Table 6. 



Table 6 may be summed up in the statement that ticked yellow 

 behaves like variegation ; for ticked yellow X clear yellow gives 50 per 

 cent ticked and 50 per cent pure yellow. Ticking differs from variega- 

 tion only in the amount of dark pigments involved. We have already 

 seen that there is probably a determiner for mottling. We now see 

 that the mottling determiner occurs in various degrees which maybe 

 designated M', M", etc. 



The question arises what determines the degree of mottling in any 

 case ? If all mottling results from a cross of yellow and green why are 

 the proportions of yellow and green so diverse ? Of the fact of this 

 diversity there is no doubt. For example, in Experiment 501 a pure 

 yellow (No. 4 female) was crossed with a pure green (No. 37 male), 

 and of two offspring one was green, except for yellow bands across the 

 back and a yellow belly and breast. The other was all yelloiv except 

 for dark eye-spots, side of breast, and base of perianal fluff. Conse- 

 quently one may speak of the mottling factor as wide in one case and 

 restricted in the other. Individual germ cells vary in the extent of the 

 spots they determine. 



