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SCIENCE 



[N. S. Vol. XLIV. No. 1134 



they belong to the same linkage group, in both 

 species. Since this happens to be the sex- 

 linked group it means in reality that three 

 corresponding factors — the sex factor, the yel- 

 low factor and the forked factor — are linked 

 in both species. Whether the same degree of 

 linkage obtains in each has not been deter- 

 mined. 



It is, of course, too early to generalize from 

 this one case, but certainly the evidence 

 strongly suggests that there is a genetic con- 

 tinuity of factorial associations in these flies. 

 And if the factors are located in the chromo- 

 somes it is equally suggestive of a genetic 

 continuity of the chromosomes. 



So far as I know this is the first clear case 

 of the kind on record, and since the work 

 promises further evidence on the same point a 

 word may be said regarding the chromosomes 

 of the species concerned. As is well known 

 Drosophila ampelophila has four pairs of 

 chromosomes — two of large euchromosomes, 

 one of shorter sex-chromosomes and one of 

 very small " m-chromosomes." In contrast 

 to this the species I am breeding has six 

 chromosome pairs, of which only two resemble 

 those in ampelophila. The latter are the sex- 

 chromosomes and the " m-chromosomes." The 

 other four pairs replace the two euchromo- 

 some pairs of ampelophila and are individually 

 about half their size. 2 



Upon the chromosome hypothesis characters 

 in this new species should fall into six linkage 

 groups instead of four. And what is of much 

 greater interest, if present indications are 

 reliable, it may eventually be possible to com- 

 pare these groups (and hence the chromo- 

 somes?) individually with those in ampelophila 

 by means of corresponding characters. The 

 first step in this comparison may be repre- 

 sented by the sex-linked characters yellow and 

 forked mentioned above. 



A more detailed report of these results will 

 be presented as soon as certain experiments 

 now under way are completed. 



Chas. W. Metz 



Station for Experimental Evolution, 

 Cold Spring Harbor, N. Y. 



2 See Metz, C. W., ' ' Chromosome Studies in the 

 Diptera," I., Jour. Mxp. Zool., 1914, p. 50. 



BACTERIAL BLIGHTS OF BARLEY AND CER- 

 TAIN OTHER CEREALS 



At the Columbus meeting of the American 

 Phytopathological Society the writers reported 

 on a bacterial disease of barley. This was de- 

 scribed as a widely occurring disease attack- 

 ing leaves, leaf sheaths and glumes, early 

 characterized by water-soaked lesions with 

 bacterial exudate, and later by the persistent 

 transparency following the death of the parts 

 invaded. The abstract of this paper appeared 

 in Phytopathology (Vol. 6, p. 98). Labora- 

 tory and field studies have now been com- 

 pleted which confirm all of the preliminary 

 statements and furnish the data for the pub- 

 lication of the causal organism as a new spe- 

 cies. It is a monotrichous rod with a single 

 polar flagellum, hence referable to Migula's 

 genus Pseudomonas. Field and laboratory 

 studies have combined to show that it is seed 

 borne, and that in this way it is readily dis- 

 seminated. This fact accounts for its very 

 general distribution, it having already been 

 collected from eight states. Not only has the 

 development of the disease been traced in the 

 field where infected seed was used, but, in 

 addition, the organism has been secured in 

 pure culture from seed collected two years 

 previously, and successful inoculations with 

 this have proved its continued virulence. 



Diseases very similar to the one on barley 

 have been found and studied on wheat, spelt 

 and rye. These have all been proved to be of 

 bacterial origin. From each of these hosts the 

 causal organism has been isolated, and its 

 pathogenicity fully determined. The organ- 

 isms from these three sources are apparently 

 all one species and they are very similar to 

 the barley blight organism. 



This similarity holds for the appearance and 

 development of the disease lesions, and for the 

 morphological and cultural characters of the 

 organisms. All like the barley organism are 

 monotrichous and yellow in culture. The 

 chief difference noted is in the behavior in 

 cross inoculations. The barley blight organ- 

 ism when inoculated on wheat, rye, spelt, oats 

 and barley, infects barley only. The wheat, 



