1 86 Blackburn and Harrison . — The Status of the British 
10. Known hybrids showed the same type of behaviour as outlined in 
paragraphs 4-9. 
11. Arguing from points 4-10 we have decided that every rose studied 
showing partial reduction was really of hybrid origin. 
12 All the abnormal roses are facultatively apomictical ; this we 
assign to the stimulus of heterozygosis. 
13. Hybridity, in this view, is likewise responsible for the wide range 
of variation in the genus Rosa. 
14. We have shown that hybridity is one of the sources of microgene 
building in the genus Rosa. 
15. This process of microgene building is probably still proceeding. 
16. Since the functional pollen grains in the supersection Caninae 
contain seven chromosomes and the egg-cell twenty-one in the Villosae, and 
twenty-eight in the rest of the Caninae, it is clear that reciprocal hybrids 
between the two named will have different chromosome numbers. 
17. Crosses within the limits of the pentaploid and abnormal tetra- 
ploid forms will have the same number of chromosomes as their parents, but, 
as in the crosses referred to in 1 6, will be strongly matroclinous. 
Literature cited. 
Almqvist, S. : Sveriges Rosae. Stockholm, 1919. 
: Rosae Musei regni suecici in methodum naturalem redactae. Arkiv for Bot., 
Bd. xvi, No. 9, 1920. 
Barclay, W. : Perthshire Roses. Trans. Perth. Soc. Nat. Sci., vol. v, Part II, 1910. 
: Our Native Hybrid Roses. Ibid., Pt. Ill, 1911. 
Boitard, M. : Manuel des Roses. Paris,, 1836. 
Digby, L. : The Cytology of Primula Kezuensis and other related Primula hybrids. Ann. Bot., 
vol. xxvi, 1912. 
Ernst, A. : Bastardierung als Ursache der Apogamie im Pdanzenreich. Jena, 1918. 
Gates, R. R. : The Mutation Factor in Evolution with Particular Reference to Oenothera. London, 
I 9 I 5- 
PIarrison and Doncaster : On Hybrids between Moths of the Sub-family Bistoninae, &c. Journ. 
Gen., vol. iii, No. 4, 1914. 
Harrison, J. W. H. : Our British Roses, their Hybridology and other Genetical Problems. Trans. 
Nat. Plist. Soc. North, and Durham, 1920. 
Holmgren, I.: Zytologische Studien iiber die Fortpflanzung bei den Gattungen Erigeron und 
Eupatorium . Kungl. Svenska Vet.-Akad. Ilandl., Bd. lix, No. 7, 1919. 
Ju el, IP. O. : Die Kernteilungen in den Pollenmutterzellen von Hemerocallis fulva und die bei 
denselben auftretenden Unregelmassigkeiten. Jahrb. f. wiss. Bot., Bd. xxx, 1897. 
— — : Die Tetradenteilung in der Samenanlage von Taraxacum. Arkiv for Bot., Bd. ii. 
1904. 
Lotsv, J. P. : Evolution by Means of Hybridization. The Hague, 1916. 
Pace, L. : Apogamy in Atamosco. Bot. Gaz., vol. lvi, 1913. 
Rosenberg, O. : Cytologische und morph. Studien an Drosera longifolia x D. rotundifolia. Kungl. 
Svenska Vet.-Akad. Handl., Bd. xliii, 1909. 
