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 the 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 plants that were either night- 
shades or tomatoes, but rarely a bud arose that had 
a core of tomato tissue and a skin of nightshade 
