Criteria for Judging Polyploidy 371 



established as a rule that ^\ill hold for all polyploids. In the above 

 cases a lew instances are cited Avhich indicate that each problem must 

 be dealt with independently according to the requirements. 



15.7: Fertility 



Two general methods are used to judge the fertility level of a 

 specific polyploid: (1) percentage of good pollen as demonstrated by 

 microscopic test, and (2) the amount of seed set. Fertility differ- 

 ences and chromosomal phenomena at meiosis have been correlated, 

 but no general rule that explains the total possibility has been estab- 

 lished. ^^ Unequal distributions of chromosomes in the meiotic stages 

 from first metaphase do cause unbalance in chromosomes in the pol- 

 len, and ultimately in the gamete. Triploids are notoriously bad with 

 respect to chromosomal balance. -^ When the percentage of pollen that 

 appears to be good is used to express the fertility ultimately judged 

 by seed production, some reservations must be made.* 



Female sterility in the ovule arises at meiosis and may or may not 

 be the same as for pollen. Some polyploids are female-sterile and 

 pollen-fertile, and vice versa. The embryo-sac stages are difficult to 

 study because an involved cytological technique is required.^ 



Among progenies of amphiploids the first generation may be quite 

 fertile, while later generations may segregate due to weak and low- 

 fertility. By successive selection the fertility level may be raised, or 

 there may be mechanisms for improving fertility by elimination of 

 those genotypes that are deficient or have no survival value. 



Perhaps no other aspect of polyploidy is more controversial than 

 this subject of fertility in the immediate product of doubling and in 

 the subsequent generations. Practically and theoretically the prob- 

 lems are unsolved at this point. 



REFERENCES 



1. Akerman^ a. (see Ref. No. 1, Chap. 11). 



2. Atwood, S. (see Ref. No. 9, Chap. 13) . 



3. Blakeslee, a. (see Ref. No. 11, Chap. 11). 



4. Brown, M. Pohploids and aneuploids deii\ed from species hybrids in Gossyp- 

 iu»i. Hereditas Suppl. \'ol. Pp. 15-16. 1949. 



.5. Chin, T. (see Ref. No. 18, Chap. 12) . 



(). Clausen, J., et al. (see Ref. No. 18, Chap. 11) . 



7. CuA, L. (see Ref. No. 20, Chap. 11) . 



8. Das, B. Cytoloy,ical and enil)rvolos^ical basis for stcrilit\ in antotctra]iloid 

 sweet clover Melilutus alba Desr. Iowa State College Jonr. Sci. 27:537-61. 1953. 



9. Dermen, H. Detection of polyploidy by pollen-grain size. (I) Investigation 

 with peaches and apricots. Proc. Anier. Soc. Hort. Sci. 39:96-103. 1938. 



10. Ek.sti. O. The effects of colchicine upon the di\ision of the generative cell in 

 Pol\o;())uitu»i. Tradescantia. and Lilium. Amer. Jonr. Bot. 27:512-24. 1940. 



11. _, AND Taylor, H. (see Ref. No. 52, Chap. 13) . 



12. EiNSET, J. (see Ref. No. 19, Chap. 14) . 



