136 CARNEGIE INSTITUTION OF WASHINGTON. 



of bristles to 4. Without having rigidly demonstrated the conclusion, 

 Dr. JMacDowell finds it probable that the variation in the number of 

 extra bristles is due to the absence of one or more accessory restricting 

 factors. 



OTHER STRAINS OF DROSOPHILA. 



To provide material for the cytological work a large number of 

 cultures of Drosophila have to be maintained. Mr. Metz has carried 

 at all times between 100 and 200 cultures and at times there have 

 been double these numbers. In attempts to hybridize different species, 

 scores of special cultures have been made up and carried on. Also, 

 mutant races have been sought and bred in species having different 

 chromosome groups. 



Mr. AlbertM. Brown, of Columbia University, spent about two months 

 of the summer at the laboratorj^ studying the linkage of characters in 

 heredity in Drosophila. Mutants with eosin-colored eyes and minia- 

 ture wings were mated to individuals of wild stock from France, 

 Australia, Central America, Cuba, and several points within the United 

 States, and the linkage of the above mutant characters was studied. 

 Over 56,000 F2 progeny were embraced in the data obtained. 



FOLIAGE COLOR OF LYCHNIS. 



The fohage color of Lychnis has been shown by Dr. ShuU to depend 

 upon the presence of several independently inheritable factors, Z, N, 

 and Y. When Z is absent albinos appear. When Z is present, together 

 with both A^ and Y, the plants are of the normal dark-green color usually 

 seen in this species. Z and N without Y produce a light-green race 

 which Dr. Shull calls pallida, and Z and Y without N produce a vari- 

 able yellowish-green race, which has been named chlorina. These 

 two light-green races produce (when crossed together) only dark-green 

 offspring, which yield F2 progenies when bred inter se, consisting of 

 dark-green and light-green individuals in approximately the expected 

 ratio 9 : 7. The last term of this ratio should include 3 pallida 

 (ZZNNyy), 3 chlorina (ZZnnYY), and 1 ''subchlorina" (ZZnmjy). 

 It was not known until this year whether such a form as subchlorina 

 could exist, and it was conceivable that the ratio of dark green to light 

 green in the Fg might be 9 : 6 instead of 9 : 7. The existence of the 

 heretofore purely hypothetical subchlorina has been demonstrated by 

 this year's cultures, as two individuals used in crosses in 1913 had the 

 subchlorina constitution. 



INHERITANCE IN CENOTHERA. 



Investigation of the hybridization phenomena in the Oenotheras 

 has been continued by Dr. Shull, and many of the F2 combinations 

 which had not been grown hitherto have been added this year, so that 

 most of the possible combinations of (Enothera lamarckiana and the 



