DEPARTMENT OF GENETICS. 109 



Cooperative Work on Datura Mutants. 



The Datura work is of such great theoretical importance that it 

 deserves all the cooperation that can be secured for it. We have 

 been very fortunate in getting such assistance, largely by volunteers 

 who have offered their cooperation without pay. Among these 

 collaborating are the following: 



Dr. E. W. Sinnott, of Connecticut Agricultural College, is studying 

 the differences in gross morphology and in histology between chromoso- 

 mal types. 



Dr. John W. Buchholz, of the University of Arkansas, has perfected 

 a rapid method of isolating pollen-tubes and of studying their growth 

 without the aid of parafhne sections. He is investigating the be- 

 havior of pollen and egg cells in the different chromosomal types which 

 may throw light upon incompatibilities between races and species. 



Dr. J. Arthur Harris, of this Department, is investigating the in- 

 fluence of the extra chromosomes upon the sap concentration by means 

 of determinations of freezing-point and of electrical conductivity. 



Dr. C. Stuart Gager, Director of the Botanic Garden, Brooklyn In- 

 stitute of Arts and Sciences, is investigating the possible effect of radium 

 emanations upon gene and chromosomal mutations. 



Mr. J. L. Cartledge, of the University of Pennsylvania, worked at 

 Cold Spring Harbor during the past summer upon the question of 

 pollen sterility. 



It is hoped that further cooperation can be secured in the coming 

 months. Especially profitable is the arrangement by which professors, 

 freed of other duties, can spend their vacations at so agreeable a spot 

 as Cold Spring Harbor at a time when the Daturas are actively grow- 

 ing and flowering. 



Non-disjunction of the Fourth Chromosome of Drosophila. 



In the course of a selection experiment with Drosophila melanogaster 

 peculiar behavior of the characters "normal eye" (N) and "eyeless" 

 (n) has been observed and studied by Dr. Little. Although no 

 cytological supporting evidence has been obtained, the genetic results 

 are best explained on the supposition that triploidy and tetraploidy 

 of the fourth chromosome have taken place. Certain additional 

 hypotheses also appear to be necessary, as follows: The reduction 

 during gametogenesis of Nnn flies is usually (although not exclusively) 

 of the Nn-n type; that of the NnNn type is random. The somatic 

 appearance of the Nnn, NnNn, and Nnnn flies is sometimes normal 

 and sometimes eyeless. The proportion of these forms which appear 

 in any given mating seems to be influenced by modifying factors. 



This suggests that the somatic appearance of these types as well as 

 the nature of the reduction division may be different in different lines. 

 As the whole matter involves detailed analysis of the genetics of the 



