462 T. H. MORGAN AND C. B. BRIDGES 



CONCLUSIONS REGARDING SPECIFIC DILUTION EFFECTS 



The most important relations that these detailed comparisons 

 have brought to light are the following : It appears that the four 

 factors involved may be arranged in the order of their specific 

 effectiveness in dilution. First comes pink; second, vermilion; 

 third, eosin; fourth, white. 



Vermilion and pink eye colors cannot with advantage be di- 

 rectly compared because of differences in the quality of the eye 

 colors. Their relative effect in dilution may, however, be com- 

 pared in the following way. Starting with eosin as a base, and 

 substituting the factors vv (vermilion) for VV, we obtain a spe- 

 cific dilution effect as the double recessive eosin vermilion. If 

 we start with eosin and substitute pp for PP a specific dilution 

 occurs giving eosin pink. A comparison of eosin vermilion color 

 with eosin pink color shows that there is little difference between 

 them — if either is lighter it is the eosin vermilion. The only 

 other way to determine the relative effectiveness of these two 

 factors in dilution is to observe which of the two becomes more 

 diluted by heterozygosity for the same combination of other fac- 

 tors. If the end results in the two cases are unequal in color, 

 the difference must be due to initial differences in the bases, for 

 the diluters added in each case are the same. If then vermilion 

 is diluted by a certain combination and pink is not, we may 

 conclude that vermilion is a greater help to dilution than is pink. 

 For instance, pink heterozygous for white shows no dilution ef- 

 fect, while vermilion heterozygous for white does show a slight 

 dilution effect. Again, pink heterozygous for vermilion and white 

 shows no effect, while vermilion heterozygous for white and 

 pink shows a distinct dilution. It follows if the validity of the 

 argument is admitted that vermilion is a slightly stronger diluter 

 than pink. 



If vermilion is used as a base and pp is substituted for PP a 

 strong effect is produced. If vermilion is used as a base and 

 ww^ is substituted for WW a still stronger dilution is produced, 

 which shows that eosin is a stronger diluter than pink. Starting 

 with pink as a base and adding vermilion we observe a certain 



