Rose Forms as determined by their Cytologkal Behaviour. 187 
Rosenberg, O. : tlber die Chromosomenzahlen bei Taraxacum und Rosa. Svensk. Bot. Tidskr., 
Bd. iii, 1909. 
* — l : Die Reduktionsteilung und ihre Degeneration in Hieracium. Ibid., Bd. xi, 1917. 
Strasburger, E. : Die Apogamie der Eualchimillen und allgemeine Gesichtspunkte die sich aus 
ihr ergeben. Jahrb. wiss. Bot., 1904. 
Tahara, M. : Cytological Studies on Chrysanthemum. II. Bot'. Mag. (Tokio), 1915. 
Tackholm, G. : On the Cytology of the Genus Rosa. A Preliminary Note. Svensk. B.ot. Tidskr., 
Bd. xiv, 1920. 
Tischler, G. : Zellstudien an sterilen Bastardpflanzen. Archiv fiir Zellforsch., Bd. i, 1908. 
Winge, O. : Studier over Planterigets chromosomtal og chromosomernes betydning. Comptes 
rendus Lab. Carls., Copenhagen, 1917. 
Wolley-Dod, A. H. : A List of British Roses. London, 1911. 
EXPLANATION OF PLATES IX AND X. 
Illustrating Miss Blackburn and Dr. Harrison’s paper on the Status of the British Rose Forms. 
PLATE IX. 
Illustrating Meiosis in the Pollen Development and the Somatic Mitoses in the Normal 
Types of Rosa. 
Figs. 1-3, 7, 10-15, an d 18-22 from Rosa arvensis. 
Figs. 4-6, 8-9, 16, and 22-25 from Rosa pimpinellifolia , and Fig. 17 from Rosa rugosa 
All the figures were drawn with the camera lucida. Mag. 4,000. 
big. 1. Pollen mother-cell previous to synapsis. 
Fig. 2. Synapsis. 
Fig* 3. Evolution of spireme from the synaptic knot. 
Fig. 4. Spireme completely expanded. 
Fig. 5. Bivalent units of spireme showing longitudinal split. 
Fig. 6-9. Stages in development of the bivalents. 
Fig. 10. Diakinesis. 
Fig. 11. Multipolar spindle stage. 
Fig. 12. Metaphase of the heterotype division. 
Fig. 13. Equatorial plate of R. arvensis showing seven chromosomes. 
Fig. 1 4. Telophase. 
Fig. 15* Interkinesis after heterotype division, 
big. 16. Metaphase of the homotype division. 
Fig. 17. Anaphase from R. rugosa. 
Fig. 18. Telophase of the homotype division. 
Fig. 19. Completed tetrad. 
Fig. 20. The four spores of the tetrad separated. 
Fig. 21. Late somatic prophase. 
Fig. 22. Somatic equatorial plate showing 14 chromosomes. 
Fig. 23. The same in R. pimpinellifolia showing 28 chromosomes. 
Fig. 24. Somatic metaphase. 
Fig. 25. Late somatic anaphase. 
PLATE X. 
Fig. 26. Synapsis in R. Sabini. 
Fig. 2 7. Spireme in R. Sabini. 
big. 28. Differentiation of bivalent loops and univalent rods in R. parisiensis . 
