244 t)l<- J- W. HESLOP. HARRISON ON 



The Genus Rosa, its ffybn'dology and other Genetical 

 Problems. 



By J. W. Heslop Harrison, D.Sc. 



I. Introductory. 



II. Orthogenesis in Rosa 



III. Pollen conditions in the Rospe, with some consideration of other 

 features in their Reproduction. 



Pollen Abortion in the Roses. 



Pollination in the Roses. 



Cleistogamy. 



Apogamy. 



Polyembryony. 



IV. The Phenhybrids of Rosa. 



History of recognised Rose Hybrids. 

 Modern Conceptions regarding them. 

 Their uneven Geographical Distribution. 

 Their Powers of producing good Seed. 

 Observations on the Hybrid Forms. 



V. List of Literature cited. 



I.— INTRODUCTORY. 



Species rosarum difficillime liniitibus circumscribuntur et forsan 

 natura vix eos posuit — T-innDeus, Species Planfaniin. 



Species rosarum ditHcillinie distinguuntur, difficilius determinantur ; 

 mihi videtur naturam miscuisse plures vel lusu ex uno plures 

 formasse ; hinc qui paucas vidit species facilius eas distinguit, quam 

 qui plures examinavit. — Linn., Species Plantanim, 1753- 



Althotigh written more than a htmdred and fifty years ago, 

 to most botanists, even of to-day, tlie above extracts from the 

 Species Plantaruni appear to be as true as Linnaeus imagined ; 

 as a natural consequence, except to the specialist, the genus 

 Rosa is more or less of a tabooed subject. 



Nor can this be wondered at when the novice beholds the 

 bewildering array of forms, seemingly alike, masquerading 

 under different names in the carefully labelled herbaria of the 

 rliodologist, or even after he has attempted to name a casually 

 collected rose by means of some flora. Both experiences are 



