PN-5865 



I^'IGURE 7. — The elongate type of tuber of D. trifida. 



sex-determining chromosome. The high numbers of chromosomes 

 confound the sex determining mechanism and lead to the produc- 

 tion of more males than females in some crosses (26). In Guade- 

 loupe, 3.6 males were found to 1 female among 225 seedlings 

 examined (9). In Trinidad, the sex ratio among seedlings was 

 found to be five males to one female. 



Cross-pollination is easily achieved when plants are grown 

 close together or are allowed to intertwine. Small flies and other 

 insects are believed to be responsible for pollen transfer in Dio- 

 scorea. Hand pollination is easily managed, and bagging the female 

 flowers before and after pollination provides control. Male flowers 

 open in the morning and begin to shed pollen about one-half hour 

 later. Anthesis proceeds irregularly along the raceme over a period 

 of 3 to 8 days. The female flower remains open and presumably 

 susceptible to pollination for several days. The capsules mature in 

 the dry season 3 to 4 months after pollination. Although most 

 crossing combinations are fertile, a few appear sterile, possibly a 

 result of differences in ploidy of the parents. 



Seeds germinate irregularly after a post-maturation rest pe- 



10 



