POLYPLOID SERIES 159 



have sLo\\m that certain groups of roses, especially those 

 belonging to the family of canina rose, are polyploid 

 types. Their differences are not only dne to polyploidy, 

 but combined mth this there is evidence of extensive 

 hybridization. 



diploid triploid tetraploid 



hexaploid ^^ ^^ 



pentaploid octoploid 



Fig. 92. 

 Polyploid series of roses. (After Tackholm.) 



Tackholm has recently made an elaborate study 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 



