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 of 
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. 
