THK GENUS ROSA 



261 





Text-fig. 2. a. Pollen of J?osa rugosa X 300. 



b. VoWen oi R.JlexibiHs X 250. 



c. Pollen of R. mollis var. caendea X 250. 



These, and other observations, by the close analogy they 

 bear to the circumstances ascertained to hold with recognised 

 hybrids, urge one strongly to the view that similarity in pollen 

 condition is correlated with similarity in genetical constitution. 

 In other words, the conclusion becomes irresistible that the 

 bulk of so-called rose species are hybrids likewise. The sole 

 difference lies in the fact that in the known hybrids their 

 condition is patent and betrayed by every point in their 

 structure, whereas in most of the roses, owing to the closeness 

 of the parent forms, the hybridity is latent. Thus it can only 

 be manifested during that delicately balanced test of parental 

 equality gametogenesis, when the lack of homology in the 

 parental chromosomes ends in the result just described, i.e., 

 pollen abortion. 



Although only a few rose microgenes were submitted to 

 cytological examination, in a much greater number the pollen 

 was critically examined and the proportion of good grains 

 determined ; what were the results the appended table 

 discloses. 



