No. 529] THE NATURE OF GRAFT-HYBRIDS 43 



an increase in the number of chromosomes in the cells of 

 the hybrid. If such a reduction does occur Cytisus 

 Adami would show the same number of chromosomes as 

 C. laburnum which has the same number as C. purpureus. 



The study of graft-hybrids has assumed a new interest 

 through the very important recent investigations of Pro- 

 fessor H. Winkler, of Tubingen. These investigations 

 prove beyond question that graft hybrids are possible, 

 and the numerous experiments carried out with every 

 possible precaution and showing remarkable ingenuity 

 as well, furnish by far the most important study on the 

 nature and origin of graft-hybrids that has yet been pub- 

 lished. These experiments are being further developed 

 by Professor Winkler but the results already obtained 

 are of the greatest interest and value. 2 



The fact that hybrids may arise as a result of grafting 

 touches some of the fundamental problems of heredity, 

 and this makes these papers of Professor Winkler of the 

 highest importance to all students of heredity, and they 

 deserve much wider attention than they have as yet re- 

 ceived. 



The plants chosen by Winkler for his experiments were 

 the black nightshade, Sohnium iiiyrum, and two varieties 

 of the tomato. Solatium lycnpcrsicuni. These two species 

 are very distinct, and indeed many botanists regard the 

 tomato as belonging to a distinct genus Lycopersicum, so 

 that Winkler's graft-hybrids might be regarded as bi- 

 generic like the Cratcego-mespilus graft-hybrids. 



The methods by which Winkler secured his graft-hy- 

 brids were extremely ingenious. Seedlings of the night- 



