266 DR. J. W. HESLOP HARRISON ON 



III addition, if tliis holds good, the converse ought to be 

 true : wherever any genus is represented in a given locality 

 by many related species their pollen, by its variable size and 

 cytoplasmic content, should suggest hybridity. Such is indeed 

 the case as has been demonstrated by Jeffery for the 

 0/iagracece, Hoar for the Rub/, Standish for the C rataegi a.wd 

 Cole for certain cultivated Hosce in America. Of these I have 

 made an independent examination of Epilobiu?n (a notorious 

 hybridiser in the Onagracece) and of the Durham Riibi, and 

 my results agree exactly with the accounts given by these 

 workers. 



Thirdly, a totally distinct consideration of the genus Rosa 

 tends to confirm the same view. If roses of such remote 

 affinities as Rosa pinipiuellifolia and R. hifet/a/ia, Rosa rugosa 

 (from Japan) and R. foliolosa (from Texas) can be successfully 

 crossed ; if such complexes as the Gottfried Keller briar com- 

 posed of ^ H. P. (Pierre Netting x Tea Madame Berard) 

 X Persian Yellow )■ x (Madame Berard X Persian Yellow) 

 can be built up; if this latter can then be crossed with satis- 

 factory results with the H. P. Charles Lefebre, what possible 

 obstacle can there be to intersectional crossing between the 

 Afzeliance, Encanina, To)iientosce, Villosce, etc., or inter- 

 microgenic crossings between the various members of any one 

 of these sections? The failure to hybridise is unthinkable. 

 Its occurrence is simply masked by the close relationship of 

 the parents and the fertility of the offspring. Only rarely 

 would it be detected otherwise than by the state of the pollen. 

 However, I have performed this feat once myself in the case 

 of a cross described later between R. Intetiaiia and R. Linfoni 

 where the hybrid, ivhich ran down in the books to the 

 duinelonan form acitulata, grew sandwiched between what 

 careful study in the field proved to be its parents. 



Another hybrid, R. mollis X R. canina forma, involving the 

 Encanince and Villosw, was brought to my notice by Traaen ; 

 this he collected under circumstances much the same at 

 Brevik in Norway. 



