The Editor: Plant Chimeras 



523 



botanists of the time feeling certain that 

 his straightforward account of its origin 

 must be a fairy tale. This particular 

 graft hybrid showed itself, when propa- 

 gated, to be inconstant in character, 

 tending to revert to one of the parent 

 forms, so it is not unusual to find a tree 

 of Cytisus adami on some branches of 

 which are borne the yellow blossoms of 

 the laburnum, on others the purple 

 blossoms of the broom, and on still 

 others a mixed form showing the influ- 

 ence of both. In this case several emi- 

 nent botanists insisted that the branch 

 used by Adam in his original graft 

 must have been taken from a sex- 

 hybrid plant, a view that has not wholly 

 been given up yet.i although hardly 

 tenable in the light of our present 

 knowledge of chimeras. 



THE WHITETHORN MEDLAR. 



The third classical example is that of 

 the medlar {Mespilus germanica) near 

 Metz, Germany, on which a branch of 

 whitethorn {Crataegus monogyna) was 

 grafted more than a century ago. From 

 the graft there grew three sprouts which 

 showed various blends of the charac- 

 ters of the two parents. The original 

 tree, references to which abound in 

 botanical literature, is still in existence; 

 its hybrid shoots when propagated show 

 a constant tendency to revert to one of 

 the parent types. 



These examples indicate how chi- 

 meras, or graft-hybrids of a pronounced 

 type, originate unexpectedly. With the 

 growth of the experimental method in 

 botany came a realization that the only 

 way to settle the problem of the origin 

 of these freaks was to produce similar 

 ones in the laboratory under controlled 

 conditions. Dr. Hans Winkler, then at 

 the University of Tubingen but now 

 director of the State Institute of Botany 

 at Hamburg, Germany, undertook the 

 task with spectacular success. 



For his material he selected the 

 tomato (Solanum lycopersicmn or, ac- 

 cording to the latest American nomen- 

 clature, Lycopersicon esculentum) and 

 the nightshade (Solanum nigrum). 

 These species are closely enough related 



1 At the Fourth International Conference on Genetics in Paris, 1911, L. Blaringhem upheld the 

 idea that it was a sex-hybrid showing mosaic inheritance. 



CALLUS TISSUE 



Cutting showing the formation of callus 

 around the edges, gradually spreading 

 inward until it covers the whole 

 wound. At this stage the callus tissue 

 is soft and translucent; later it hard- 

 ens and from it arise roots, if the 

 cutting is planted (as in this case) 

 or shoots, if the cut is above ground. 

 From such sprouts plant chimeras 

 are obtained. Photograph enlarged 

 eight diameters. (Fig. 2.) 



to be handled conveniently, and yet 

 differ markedly enough in general ap- 

 pearance to be identified easily by com- 

 parison. He grafted them on each 

 other, reciprocally, using the common 

 cleft or saddle graft, and after the graft 

 had "taken" he cut through the stem of 

 the plant at the point of graft, in such 

 a way that the surface exposed con- 

 tained sections of both parents (see fig. 

 4, A. B. and C.). The wound healed 

 over with the formation of a callus, and, 

 as usual, sprouts or "adventive shoots" 

 grew up from it. Some of these sprouts 

 grew from the part of the surface con- 

 taining tomato plant tissue, some from 

 that part containing nightshade tissue. 



