POLYPLOID SERIES 169 



ration divisions. It is suggested that a comparable series 

 of changes may exist in the egg mother cells and lead to 

 the retention of all the chromosomes in the parthenoge- 

 netic egg-cells. 



In the cultivated varieties of chrysanthemum, Tahara 

 has found a polyploid series. In ten varieties (Fig. 97) 

 nine haploid chromosomes are present, but the chromo- 

 somes themselves have different sizes, and, more impor- 

 tant still, the relative size of the chromosomes may be 

 different in different species (Fig. 98). This point will be 

 considered later. It is also significant that the nuclear 

 size may be different in some of these cases where the 

 total number of chromosomes is the same. Other species 

 of chrysanthemum have multiples of nine (Fig. 99) ; two 

 species have 18, two have 27, one has 36, two have 45. The 

 following table gives the relation between chromosome 

 number and nuclear size. 



Triploid varieties of the mulberry (Morus) have been 

 reported by Osawa. Of the 85 varieties studied, 40 are 

 triploids. The diploid number of chromosomes is 28 (n= 

 14) and the triploid 42 (3X14). The diploid plants are 

 fertile, while the maturation divisions of the triploid 

 show irregularities (univalent chromosomes) and have 

 abortive pollen grains and embryo sacs. In the first matu- 



