THE CHROMOSOMES * 177 



The tissue of the sporophyte is capable of re- 

 generating if a piece of it is kept under proper 

 cultural conditions. Its cells do not regenerate 

 another sporophyte but instead a sexual moss- 

 plant, or gametophyte, which now has the diploid 

 number of cells, since it arose directly from sporo- 

 phyte tissue. These diploid gametophytes give rise 

 to antherozoids (without reducing) and to female 

 oospheres (without reducing). Therefore by the 

 union of the two a tetraploid sporophyte is pro- 

 duced. In a few mosses, octuploid sporophytes 

 have been produced, by starting with a tetraploid 

 sporophyte and repeating the procedure just 

 described. 



Tetraploid plants of the tomato (Solanum 

 lycopersicum) and of tlie nightshade (Solanum 

 nigrum) have been artificially produced by Winkler 

 by means of the same kind of grafting experiments 

 that had produced periclinal chimaeras in his earlier 

 work. A piece of the nightshade was grafted onto 

 a tomato stock by a wedge-shaped union. After 

 union had taken place the combination was cut 

 across at the level of union in such a way that the 

 tissue of the nightshade was exposed on each side 

 of the cut surface and that of tomato in the middle 

 of the surface. If at the same time all the axial 

 buds were removed from -such a piece new adven- 

 titious buds appeared on the cut surface. Most of 

 these gave rise to i)lants that were eitlier night- 

 shades or tomatoes, but rarely a ])ud arose that had 

 a core of tomato tissue and a skin of nightshade 



