PLANT CHIMERAS 



By MACGREGOR SKENE, B.Sc. 

 Lecturer on Vegetable Physiology, Aberdeen University 



The practice of horticulture and the study of heredity have led 

 to the production of innumerable hybrids, plants having their 

 origin in the fused sex-cells of two distinct races, species, or 

 even genera, and frequently betraying their dual nature by ex- 

 hibiting characteristics of both parents. From these legions of 

 intermediate forms, as to the sexual origin of which there is no 

 doubt, there stand apart a very few isolated cases of hybrids 

 which seem to have arisen in another fashion. By reason of 

 their supposed mode of origin they have long been labelled 

 graft-hybrids; and both because of this origin, which was 

 doubtful, and because of various peculiarities which they con- 

 stantly exhibited, a considerable amount of attention has been 

 paid them during the last eighty years or so. Only five years 

 ago, however, did the various problems involved prove capable 

 of an experimental solution. Professor Winkler, of Hamburg, 

 has succeeded in replacing the airy castles of theory by an 

 edifice built of solid fact enough, but of a nature more curious 

 than that of any of its predecessors. 



The most notable of the so-called graft-hybrids is the shrub 

 known as Cytisus Adami, which is supposed to have arisen in 

 the following way. It is a common practice of gardeners to 

 graft the purple broom, Cytisus purpureas, on to the laburnum, 

 Cytisus Laburnum. Cytisus purpureus bears on its spiky stems 

 many tufts of fine purple flowers, but the stems are low-growing 

 and the plant makes no great show. Grafted on the laburnum, 

 however, it artificially raises its purple head and thereby greatly 

 enhances its decorative value. In the year 1829 the Parisian 

 gardener Adam observed that a bud from one of these grafts 

 had produced a novelty. The flowers on the new shoot were 

 indeed purple in colour, but instead of occurring in small erect 

 tufts they occurred in the fine drooping clusters so characteristic 

 of the laburnum. In other words, the inflorescence exhibited 



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