POLYPLOID SERIES 159 



have shown that certain groups of roses, especially those 

 belonging to the family of canina rose, are polyploid 

 types. Their differences are not only due to polyploidy, 

 but combined with this there is evidence of extensive 

 hybridization. 



*7V* C 9 t(r> 



diploid triploid teLraploid 



jy&/t 



W 



hexaploid 



pentaploid octoploid 



Fig. 92. 

 Polyploid series of roses. (After Tackholm.) 



Tackholm has recentlv made an elaborate studv of 

 these roses. His account may first be followed. The spe- 

 cies with 14 chromosomes (n=7) have the smallest num- 

 ber, and may be taken as the basal type. There are trip- 

 loids (3 times 7), tetraploids with 28 chromosomes (4 

 times 7), pentaploids (5 times 7), hexaploids with 42 (6 

 times 7), and octoploids with 56 (8 times 7). See Fig. 92. 

 In the maturation division of some of these polyploids 



