614 



THE AMERICAN NATURALIST [Vol. XLIV 



plant and other Thymelacea?, point rather towards 

 apogamy than parthenogenesis. 



Even more perplexing to the stndent of sex and hered- 

 ity than apogamy or parthenogenesis are the phenomena 

 presented by what are known as graft hybrids. A 

 number of seed plants of a hybrid nature are known 

 to botanical science, which have not arisen by means of 

 seed production, bnt presumably from the callus formed 

 at the juncture of the stock and scion in grafting. The 

 most noted of these is, of course, Cytisus Adami, which 

 is supposed to have arisen from Cytisus laburnum and 

 Cytisus purpureus as a graft hybrid. This problem, 

 which has held, in a large measure, the interest of biol- 

 ogists for about eighty years, seems now to be on a fair 

 way towards a solution, having as a starting point the 

 production of a graft hybrid experimentally. Hans 

 Winkler, as is well known, has produced a plant which, 

 in point of flower, fruit and foliage, seems to be a hybrid 

 between the common nightshade Solatium nigrum L. and 

 the tomato, Solarium lycopersicum L. of the King Hum- 

 bert yellow-fruited variety, by an ingenious method of 

 grafting in which the nightshade was used as the stock 

 and the tomato as the scion. Perhaps a very brief state- 

 ment of the process may not be out of place here. 



Using the cleft method of union, Winkler grafted 

 vigorous shoots of the seedling tomato upon the stem of 

 the nightshade. As soon as union had taken place the 

 scion was cut off near its base in such a way that the 

 apical cut surface consisted partly of nightshade and 

 of tomato tissue. Of the adventive shoots arising 

 only those which sprang from along the line of union 

 of the two specifically different tissues were allowed 

 to grow. In one particular case fourteen of such sprouts 

 were removed and transplanted as cuttings. Of these 

 eight proved to be Solarium nigrum, five pure Sol- 

 atium lycopersicum, and one the hybrid in question. 

 This plant grew to flower and fruition, and as stated in 

 the foregoing, revealed hybrid characters in stem, leaf, 

 flower and fruit. This hybrid Winkler named Solarium 



