PLANT CHIMERAS 129 



probable, or as improbable, as that in one isolated instance an 

 ovule of laburnum had been fertilised by pollen from the purple 

 broom giving a seed of hybrid origin : that this latter is the true 

 explanation was Dr. Vries's belief. 



We must encounter, too, the difficulty of explaining the 

 mechanism by which hybridisation during grafting could take 

 place. The stock never influences the specific characters of the 

 scion. The more luxurious growth of a delicate scion placed on 

 a sturdy stock is due solely to an improved food supply. Prof. 

 Winkler in an exhaustive memoir ("Pfropfbastarde," Part I.) has 

 shown that there is no well-authenticated case of a specific 

 change in stock or scion resulting from the influence of the 

 co-partner. There remained, seemingly, the supposition that 

 a fusion of cells of the two parents had given rise to an 

 organism bearing the characters of both. But without definite 

 proof it is not possible to believe that ordinary vegetative cells 

 of two highly organised seed-plants could assume the characters 

 of sex-cells. 



One line of evidence, the nature of its progeny, might have 

 led to a solution ; but Cytisus Adami is sterile. In the long 

 course of its history it has produced two seeds, and both grew 

 up into typical laburnums. But the number is far too small to 

 make it permissible to draw conclusions from this fact. 



Cytisus Adami is the best known and most widely distributed 

 " graft " hybrid. But one or two other similar cases are known. 

 Of these we may mention the hybrids between the hawthorn 

 and medlar to which the name Cratcegomespilus has been given. 

 Of these no less than three are known ; one is intermediate 

 between the two parents, of the two others one resembles more 

 closely the hawthorn, the second the medlar. Their origin is 

 shrouded in even greater mystery than that of the Cytisus 

 Adami; but it is equally certain that the parents are mutually 

 sterile, and that the hybrids produce vegetative throwbacks. 



When Prof. Winkler commenced his investigations some 

 seven years ago our knowledge of the origin of these curious 

 plants was sadly indefinite. That they had arisen by grafting 

 seemed improbable ; that they possessed properties seen in no 

 other hybrids made a sexual origin equally doubtful. 



Prof. Winkler saw that it was useless to attack the problem 

 by grafting laburnums or hawthorns ; that had been tried times 

 without number, with uniform lack of success. He looked 



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