176 THE CHROMOSOMES 



nuclear and cell division. Second, that it comes 

 from the union of two gametes each with the un- 

 reduced number of chromosomes. Third, that such 

 plants do not arise from the egg itself, but as bud 

 sports from cells that had the diploid number ol 

 chromosomes. There is somewhat better evidence 

 in favor of the second view than of the other two. 

 Whatever its origin, O. gigas breeds true in the 

 same sense as does the parent type, its germ-cells 

 having the double number of chromosomes after 

 reduction. 



Gigas forms of Primula have appeared under 

 cultivation. Gregory has found some of these to 

 have tetraploid chromosomes. In other cases a giant 

 has appeared as a bud sport in the hybrid form 

 Primula Kewensis. 



Tetraploid individuals have been artificially pro- 

 duced in mosses by the Marchals. In mosses there 

 are two generations that alternate — the sexual 

 generation that produces eggs and sperm, and the 

 sexual spore-bearing generation that arises from the 

 fertilized egg. The cells of the sexual moss-plant, 

 as well as the egg-cells and sperm that it produces, 

 have the haploid number of chromosomes. After 

 fertilization the egg contains the diploid number of 

 chromosomes, and since it gives rise to the sporo- 

 phyte, this also has the diploid number of chromo- 

 somes in all of its cells. The spores are formed by 

 two divisions, and one of them must be a reduction- 

 division, since each spore has the haploid number of 

 chromosomes. 



