Till': flKNlIS ROSA 277 



A careful comparison of the degree of aporaixis witli the 

 position of the affected forms in Table I., giving statistics for 

 pollen abortion, tends to emphasise the very close connection 

 between the two phenomena; almost without the faintest 

 possibility of error they are the coupled effects of a common 

 agency. 



Now arguing from the analogy of known or patent plant 

 hybrids, either produced artificially or detected in the field, 

 we have urged that pollen abnormalities in Rosa and genera 

 similarly affected depend on hybridity in a latent condition, 

 or at least in a state not readily determined as such. This 

 view was strengthened by the discovery that a dtiinetoi-uin 

 form, classed as R. var. aciculafa, was in reality a cross 

 between R. var. Lin font and R. lutetiaua, and that its pollen 

 was exceptionally bad. Carrying the argument to its 

 legitimate conclusion, we are compelled to take up the view 

 that in the Rosce apogamy, or whatever form of apomixis they 

 present, is a phenomenoii originating in hybridity — an opinion 

 advanced from other data by Ernst. 



Quite recently Gates has attempted to show that apogamy 

 was intimately bound up with tetraploidy and octoploidy, 

 whilst earlier Strassburger and Rosenberg, formulating the 

 same idea in a cruder form, tried to trace a connection 

 between apogamy and a high chromosome number both in 

 species of the present genus and in those of related genera. 

 In particular, Rosenburg insisted that the Rosa species with a 

 haploid number of eight chromosomes — R. livida, R. cinna- 

 momea, and certain R. caniiia forms — were " sexual," whilst 

 those with 16 — R. canina var. persalicifolia and R. glauca 

 — were apogamous. In the first place, Rosenberg's figures are 

 absolutely fallacious. Every* rose I have examined apper- 

 taining to the TovientostE, Afzelia/ia;, Euca)iince and Rubigiiiosce 

 has been endowed with a diploid number of thirty five, and is, 

 therefore, pentaploid, whilst the Villosce and PiinpinellifoHcR 

 possess twenty-eight, and are thus tetraploid, as Rosenberg 

 would have discovered had he pursued their cytology further. 



* Except a dubious example possibly referable to the Rosa stylosa. 



G 



