390 



SCIENCE 



[N. S. Vol. LII. No. 1347 



therefore among the normals 8 purples to 1 

 white, and among the Poinsettias 9 purples to 

 no whites. The expectation of an equal 

 number of normals and mutants is practically 

 never realized, probably because of differential 

 mortality in early stages favoring the normals. 



A simplex purple heterozygote with the 

 formula Ppp should have the following female 

 gametic formula: P -|- 2p + 2Pp + PP- Its 

 effective male gametes should be P + 2p 

 Selfing a simplex purple heterozygote there- 

 fore should give offspring showing a ratio of 

 purples to whites in normals of 5 :4 and in 

 the Poinsettias of 7:2. Several Poinsettia 

 plants of these two heterozygous purple types 

 have been selfed and found to give color 

 ratios in their offspring in close agreement 

 with the calculated values above. When 

 Poinsettia mutants are made heterozygous for 

 the other known. Mendelian factors, segrega- 

 tion occurs in normal manner giving the 

 customary 3 :1 ratio for the characters in- 

 volved, in both normals and Poinsettias. 



Two of the 12 mutants have each a single 

 varietal type, which may be due to factors 

 modifying the expression of the more typical 

 complex. In addition two new mutant forms 

 have arisen each of which in appearance seems 

 to be a combination of two of the typical 12 

 recurrent mutants. It has not been possible 

 as yet to count their chromosomes nor to 

 study their breeding behavior. 



We have discussed the duplication of a 

 single chromosome from only one of the 12 

 sets, producing mutants with 25 somatic 

 chromosomes, with 3 chromosomes in one set 

 and 2 chromosomes in the other 11. We have 

 obtained in addition the duplication of a 

 single chromosome from each of the 12 sets 

 producing a mutant triploid for all the 12 

 homologous sets. 



The duplication may bring about a doub- 

 ling of all the chromosomes, producing Gigas- 

 liie tetraploid mutants — the "New Species" 

 type already mentioned. Such tetraploid 

 plants have presumably 48 chromosomes in 

 somatic cells and 24 in the gametes. Prom a 

 study of the color ratios in over eight thou- 

 sand oilspring from tetraploid plants, it is 



possible to assert with some confidence that 

 independent assortment of the chromosomes 

 in the homologous sets of such tetraploid 

 mutants is the rule. Selfed duplex purple 

 heterozygotes throw 35 purples to 1 white, 

 while the back-cross gives a ratio of 5 :1. 

 Simplex purple heterozygotes on the other 

 hand give 3 :1 ratios when selfed and 1 :1 

 ratios when back-crossed. 



Evidence is at hand which indicates that 

 we may have plants with other of the theoret- 

 ically possible combinations of chromosomes 

 than those mentioned in the present paper. 



The significance of the findings in Datura 

 in relation to the peculiarities in inheritance 

 in Gigas and other mutant types in QiJnothera 

 will be pointed out later. It is hoped that 

 it may be possible to publish in the near 

 future a series of more detailed papers on the 

 phenomena of chromosomal duplication in 

 the Daturas. The present preliminary publi- 

 cation will suffice to emphasize the distinction 

 which must be kept in mind between chro- 

 mosomal mutations and mutations affecting 

 only single genes. 



Albert F. Blakeslee. 

 John Belling, 

 M. E. Earnham 



Caenegie Station foe 

 Experimental Evolittion 



THE AMERICAN CHEMICAL SOCIETY. 



DITISION OF BIOLOGICAL CHEMISTET 



E. A. Gortner, chairman 

 A. W. Dox, secretary 



The fat soluble A. vitamine and xerophthalmia: 

 A. D. Emmett and Marguerite Stdrtevant. The 

 authors agree with McCoUum that xerophthalmia is 

 a disease which is due primarily to a lack of the 

 fat-soluWe A. vitamine. Experiments with rats 

 fed on different planes of nutrition, aJl with, the 

 same precautions as to sanitation, eliminate the 

 idea that xerophthalmia is primarily infectious as 

 Bulley claims. The disease can not be cured by 

 local treatment. It responds quickly to treatment 

 per OS with extracts containing the fat-soluble A. 

 vitamine. It is not contagious. It is primarily a 

 deficiency disease which in turn may bring about 

 secondary infectious conditions. 



Biochemical changes in the flesh of heef animals 

 during partial starvation: C. E. Moulton. Pat 



