2i8 THE BEHAVIOUR OF POLYPLOIDS 



C. Pentaploids 



1 . Wild Species : — 



Tulipa Clusiana (12) .... Newton and D., 1929 (Figs. 



60-61). 

 Ochna serrulata (7) . . . . Chiarugi and Francini, 1930. 



Agave sisalana (30) .... Doughty, unpub. 



2. Mutant of Species : — 



Crepis tectorum (5) . • • • Navashin, 1926 (Fig. 13). 



D. Hexaploid 



2. Mutant of Species : — 

 Rumex acetosa (8) . . . . Yamamoto. 1935. 



E. OCTOPLOID 



I. Wild Species : — 

 Crepis biennis (5) .... Collins, Hollingshead and Avery, 



1929 ; cf. Babcock, and Cameron, 



1934. 



The triploids form a majority of trivalents, the tetraploids a 

 majority of quadrivalents. The higher configurations possible in 

 the pentaploids necessarily make the kind of association more 

 variable, but it is characteristically different from that in 

 allopentaploids. Thus in pentaploid Triticum and Nicotiana 

 (Kihara and Nishiyama, 1930 ; and Webber, 1930) four chromosome 

 sets are associated as pairs, and the fifth is chiefly unpaired, although 

 they may take part in trivalents (Brieger, 1928 ; Table 29). A 

 pentaploid hybrid species of Agropyrum is presumably of this type 

 (Simonet, 1934). Chromosome behaviour in the pentaploid species 

 Ochna serrulata, Agave sisalana and Tulipa Clusiana is entirely 

 different. They both form a high proportion of multivalents 

 (Fig. 74). A new mutant autopentaploid (such as that found by 

 Navashin, 1926, in Crepis capillaris) has not yet been examined for 

 comparison, but from what we know of the behaviour of auto- 

 triploids and tetraploids, these pentaploids must be of this kind. 

 It is, however, possible on cytological grounds that they consist of 

 five sets, equally (and not strongly) differentiated. These species 

 are sexually almost sterile, the one reproducing by apomixis, the 

 other by suckers and by bulbs. They are clonal species. 



This last class of polyploids includes high multiples, which 

 probably always have different degrees of relationship between 

 different sets, for two reasons : the complexity of their origin and 

 the lower effectiveness of balance in acquiring constant allopoly- 

 ploidy. The characteristic of these species is variability in the 



