INDUCED POLYPLOIDY 1 63 



reduced fertility among tetraploids. If the crop depends on seed production, 

 then fertility levels are directly related to yield factors. A low-fertility tetra- 

 ploid cannot be expected to yield as well as the high-fertility diploid unless 

 the greater-sized seed from the tetraploid offsets the reduced numbers of 

 seeds. Along with reduced fertility, longer growth period, vigor, and physio- 

 logical factors go with tetraploids. Sometimes the new feature is an advantage, 

 and sometimes a disadvantage. The ultimate success of any tetraploid de- 

 pends upon balance in favor of tetraploids as offset by the disadvantages in- 

 cluded therewith. Sometimes the advantages and disadvantages can be cor- 

 rectly assessed before the experiment is begun (Eigsti and Tenney, 1942). 

 When the disadvantages outweigh the advantages there can be little hope 

 for practical success. Amphidiploidy offers a way to overcome the disadvan- 

 tageous sterility barrier. Whenever possible such hybrids need to be used. 



The testing procedures need consideration. For example, tetraploid rye 

 cannot be grown beside diploid rye in order to measure relative perform- 

 ances because the diploid pollinates the tetraploid, and the subsequent triploid 

 grains being sterile, the yield of the tetraploid is greatly reduced (Muntzing, 

 1951). In these cases, special designs for test are necessary. Also, it is neces- 

 sary that triploid watermelons be cultivated with some degree of care in the 

 early growth period, otherwise the performance of triploids will fall below 

 the parental types (Kihara, 1952). These and many other signs of caution 

 need to be heeded. 



SUMMARY 



Since polyploids are so important in practical agriculture and since poly- 

 ploidy is one of the methods of species formation, the future study with in- 

 duced polyploidy holds many good opportunities for crop improvement as 

 well as more information as to ways that new populations originate in nature. 

 The tool for making pol3^1oids has been found; the end of its usefulness is 

 by no means totally in sight. 



LITERATURE CITED 



Beasley, J. 1940. The production of polyploids in Gossypiwn. Jour. Hered. 31:39- 



48. 

 Belling, J. 1925. Production of triploid and tetraploid plants. Jour. Hered. 16:463- 



466. 

 Blakeslee, a. 1937. Dedoublement du nombre de chromosomes chez les plantes 



par traitement chimique. C. R. Acad. Sci. Paris 205:476-479. 

 AND A. Avery. 1937. Methods of inducing doubling of chromosomes in 



plants. Jour. Hered. 28:393^11. 

 Clausen, J., et al. 1945. Experimental studies on the nature of species. Carnegie 



Inst. Wash., D.C., Publ. 564:1-174. 



