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THE AMERICAN NATURALIST [Vol. XLIV 



graft-hybrids. Winkler's histological studies on "Sola- 

 tium tubingense" have not yet been made public, but all 

 the facts thus far seem to indicate that so-called graft- 

 hybrids, including Laburnum Ad ami, the Bizzarrias and 

 those of Mespilus, etc., are only vegetable chimeras. 



At the juncture of stock and scion in grafts, especially 

 in the case of those that produce adventitious shoots of 

 such remarkable cha factor, there is a cell complex formed 

 of the vegetative cells of two specific individuals, and 

 the specifically different cells may be regarded as being 

 so intermingled and reacting upon each other in such 

 a manner as to produce adventitious shoots of an almost 

 exact hybrid character in so far as vegetative marks are 

 concerned. In the case of Winkler's "Solatium tubin- 

 gense," whose seeds gave only pure nightshades, it is 

 clear that both egg and pollen were descended from pure 

 nightshade cells, as the nightshade and the tomato do 

 not cross. 



Although the problem of the so-called graft hybrids 

 can not be regarded as definitely settled, yet nearly all 

 the facts go to strengthen the view that hybrids are 

 formed only by the union of cells and nuclei sexually 

 differentiated, and that fecundation and the transmis- 

 sion of characters are not accomplished by the proto- 

 plasm in general, nor by the action of an enzyme, nor 

 is it the expression of metabolism, but by the union of 

 specific material entities in the sexual nuclei. 



Although the concensus of opinion among biologists 

 attributes to the nucleus by far the most important role 

 in the process of sexual reproduction in its fullest sig- 

 nificance, yet there is still some difference of opinion in 

 regard to the relative functions of nucleus and cytoplasm 

 in imparting the stimulus to growth and cell division, 

 and in the transmission of parental characters— the two 

 chief constellations of phenomena following the sexual 

 act. 



of existing literature, a careful ;m;il\ sis ,,f ,.«.]] structure 

 and of the functions more directly concerned is neces- 



