The Origin of Species 341 



nized. Kolreuter emphasized the importance of 

 crossing, and also enunciated the principle that 

 variability was very much increased by crossing 

 hybrids, either with each other, or with the parent 

 form. 



Graft Hybrids. There has been much contro- 

 versy as to the possibility of hybrids arising from 

 grafting. Several cultivated forms are alleged to 

 have so arisen, but further attempts to reproduce 

 them in this manner have been unsuccessful, and 

 the question is still open whether the best-known 

 cases of such alleged graft hybrids, the Cytisus 

 adami and the Crataegomespilus, are not really 

 hybrids of the usual type. 



That hybrid grafts are possible has recently been 

 shown by Winkler (" Berichte der Deutschen Bo- 

 tanischen Gesellschaft," 1907), who succeeded in 

 producing an unmistakable hybrid by grafting a 

 nightshade, Solamim nigrum, upon a tomato. After 

 the nightshade graft had united with the stock, the 

 latter was cut off so as to expose a flat surface, 

 which included the united tissues of the scion and 

 stock. From this cut surface there arose numerous 

 adventitious buds, one of which developed into a 

 shoot which was a compound of the tomato and 

 nightshade. It was a " mosaic," one half being 

 tomato, the other half nightshade, and some of the 

 leaves were intermediate. Winkler proposed the 

 name " Chimsera " for such vegetable monsters as 

 this. Later experiments resulted in the production 



