284 DR. J. W. HKSLOP HARRISON ON 



its prickles, earlier white flowers, and sinooth peduncles, etc. 

 This form occupied a great area, and if it were a hybrid as 

 Schultz asserts, one would scarcely anticipate its being more 

 abundant than its parents." 



Once again we learn that the stimulus imparted by 

 heterozygosis had sufficed to emphasise an origin correctly 

 determined from other considerations to be hybrid, but that 

 lack of knowledge of such an impulse had caused its 

 indications to support the opposite view. 



Baker in the same way recognised the true affinities of fiis 

 plant for he says, " I cannot tell whether this is more Wke Sa/^//n' 



or rubiginosa It comes very near to the French 



Rosa bitiirigensis!' Recollecting that Sabiiii\% a. pi/nJ>ine!l(folia- 

 toinenfosa hybrid, we are bound to confess that this closely 

 approximates the truth, although the resemblance to Sabini 

 caused its description as an '' iiivoliita" form. 



In spite of all these shrewd surmises, it was left to Crepin to 

 point out 25 years ago the exact value to be attached to these 

 plants, and his opinion was confirmed by Marshall's discovery 

 of a bifitrigensis form in Kent, which could only arise from a 

 crossing between the Riibigiuosce, and PiinpineUifolicc. A little 

 later, in 1897, Barclay gathered the same hybrid in Perthshire, 

 and further repeated his good luck at Port Seaton, in 

 Haddington, in 1910. In addition. Prof. Traill detected the 

 same plant at Turriff in Aberdeenshire, as did Miss Hayward 

 at Melrose. 



Here again the powerful stimulus of heterozygosis had 

 played its part, and, to such an excellent observer as Barclay, 

 the fact caused much thought. I cannot do better than quote 

 his exact words in discussing his find. " I had the good 

 fortune to fall in with a rich colony of the hybrid, consisting 

 of twenty or thirty great clumps spread over nearly 

 a' mile of the coast. ... It has often been 

 remarked that hybrid plants frequently excel their parents 

 in size and vigour. Tiiis was strikingly exemplified at 

 Port Seaton. The hybrid tliere forms magnificent bushes, 



