286 DR. J. W. HESLOP HARRISON ON 



and R. coriifolia (agg.) are boreal groups, the second parent is 

 bound to be either a canina or a duiiieto)um form. Should 

 the leaflets be hairy beneath, then dinnetoruin is the second 

 parent; if glabrous, then caniiia; which microgene of either is 

 not determinable except under specially favourable conditions 

 in the field, or when very striking features characterising any 

 special microgene reappear in the hybrid. 



Matters in Scotland, Ireland and in the North of England 

 generally are on a diflterent footing. In these localities all 

 four aggregates flourish, so that hairy leaflets simply assert 

 tliat the plant is either dumetoniin Y^pimpinellifolia, or coriifolia 

 Xfiimpineliifolia; glabrous leaflets, or the contrary, imply 

 glmica or canina X pimpinellifolia. Fortunately enough, 

 seclusion of special forms in mountainous districts, or in coast 

 ravines, occasionally assists in a diagnosis ; so, too, does the 

 almost universal impotency of glauca pollen. Therefore, 

 whilst the occwxxenct'^- oi a. glauca x pimpinellifolia Ocinuot be 

 referred to as impossible, any glabrous hibernica, no matter 

 where gathered, is almost certainly the product of a crossing 

 between i?. pi/npinellifolia and some canina microgene. 



Again, but rarely indeed in my experience does any 

 coriifolia form come into contact with pimpinellifolia, so that 

 the matter is narrowed down to circumstances not differing 

 widely from those in the south. Nevertheless, in one or two 

 ravines on the Magnesian Limestone in Durham, the rose 

 flora comprises only Rosa mollis, R. coriifolia \a.x.frntetorum, 

 and R. pimpinellifolia var. spinosissima. Any so-called 

 hibernica there must be generated from the setose-peduncled 

 form of R. pimpinellifolia and R. var. frutetorum, as in the , 

 case of the specimen figured in Plate XII. 



With Rosa involuta and its allies matters are complicated in 

 much the same way. Cbrist, as we mentioned, looked upon 



* On May 291)1, 1920, I discovered an uiidoubled j^lanca X l^i'iipiiielli- 

 yiV/i< 'in a ledge just under a raven's nesl on Falcon Clints, Co. Durham. 

 The only Rosa at tlial elevation (1,600 feet) were R. piinpinellijolia and 

 K. j^laiica (forma 1). 



