POLYPLOID SERIES 



161 



each kind. Only 7 bivalents appear and 14 single chromo- 

 somes. At the first division the 7 bivalents split, the 14 

 singles do not divide and are distributed irregularly. 



In other hybrids there are 35 chromosomes (7 times 5). 

 At maturation there are 7 bivalents and 21 single chro- 

 mosomes (Fig. 93). Both behave as in the last case. 





a ~ c 



Fig. 93. 



First maturation division of a thirty-five chromosome heterotypic 

 rose. (After Tackholm.) 



In a fourth type of hybrid there are 42 chromosomes 

 (7 times 6). At maturation there are again only 7 biva- 

 lents, and, here, 28 single chromosomes. The behavior of 

 the chromosomes at maturation is the same as before. 



These four types of "hybrid roses" are classified 

 below in tabular form in regard to their pollen formation. 



7 bivalent and 7 single chromosomes. Whole number 21 

 7 bivalent and 14 single chromosomes. Whole number 28 

 7 bivalent and 21 single chromosomes. Whole number 35 

 7 bivalent and 28 single chromosomes. Whole number 42 



The unique behavior of these hybrids consists in the 

 conjugation of only 14 chromosomes to give the 7 biva- 

 lents. These chromosomes, we must suppose, are identi- 



