ROSE APHIDS. 5 



The green rose aphid was studied last year only in the partheno- 

 genetic form and the winter egg, and as there was some doubt as to 

 the number of chromosomes, it did not appear in the published results. 

 As in the case of the brown rose aphid, males are scarce, but some 

 drawings were obtained from aceto-carmine preparations and from a 

 few good sections. The number of chromosomes, seven in the sperm- 

 atocyte (figs. 7-9, 11, 13, 14), shows this to be a distinct species, as 

 had been indicated by experiments with the two kinds in the green- 

 house. All of the forms of this aphid are green, and the freshly laid 

 eggs are colorless. 



Figures 7 to 9, drawn from aceto-carmine preparations on November 

 14, show the equatorial plate of the first spermatocyte. The amount of 

 chromatin may not vary greatly from that in the corresponding cells 

 of the brown aphid, but it is differently distributed. Figure 10 is a 

 prophase of the first spermatocyte mitosis showing the side to side 

 pairing of homologous chromosomes. Figure 11 is a metaphase of 

 the first spermatocyte from a section, and figure 12 a late anaphase 

 showing the lagging pair of chromosomes — characteristic of the first 

 spermatocyte spindle in all of the species studied. Figures 13 and 14 

 are equatorial plates of the second spermatocyte, showing the same 

 number and proportionate size of chromosomes as in the first sper- 

 matocyte. In figure 15 is shown the double series of 14 chromosomes 

 in a two-cell stage of the parthenogenetic egg. This is also seen in 

 figures 1 6a and 16b, two sections of the germinal vesicle of a partheno- 

 genetic egg nearly ready for maturation. At this stage, as also in the 

 prophase of segmentation mitoses, the chromosomes are larger and 

 more irregular in outline than in the equatorial plate of the spindle. 



The third, or migratory rose aphid, has so far yielded no results 

 except from the winter eggs, which have been laid in considerable 

 numbers on isolated rose bushes in the greenhouse. Only one polar 

 spindle was found and that was cut diagonally. The nine chromo- 

 somes are shown in figures 17a and 17$; these, however, together 

 with figures 18 and 19, equatorial plates of segmentation spindles of 

 the winter egg, show the number and size relations of the chromo- 

 somes. The two broader and much longer chromosomes are without 

 doubt homologous paternal and maternal elements, and the sixteen 

 shorter ones can easily be paired. 



Thus it appears that these three species of rose aphids are as dis- 

 tinctly separated by differences in number, form, and size of chromo- 

 somes (figs. 5, 15, 18) as they are by differences in external character- 

 istics of form, size, and color. 



