326 Colchicine 



sons for this appeal oi larger (lowers are easily understood. One 

 hundred and nine varieties chosen by iris fanciers from a total of 12 

 best selections were studied for chromosome numbers. Not one was 

 dijiloid. but 108 were tetraploid, and one was triploid. Practically 

 all these were developed and selected without studying chromosomes, 

 but in this case the potential of polyploids was forcefully demon- 

 strated."'-' 



It is no surprise to find many persons attracted to the possibilities 

 to be gained from colchicine. Larger flowers were anticipated. 



Among the first colchicine-induced tetraploids to be distributed 

 were snapdragon, phlox"'-, and marigold. VV^ork with carnation-'"', 

 poinsettia-"", day lilies-'-', and lilies''^ has yielded tetraploids. There 

 are numerous projects under way with many ornamentals, annuals, 

 perennials, and shrubs. Improved flower size, darker and more com- 

 pact plants, with greater drought resistance were obtained with tetra- 

 ploid J'nud rosea LJ""' Also the llo\\'ering period was extended longer 

 than in the diploid. While seed production was reduced, this disad- 

 vantage was balanced with other positive characters in the tetraploid. 



1 3.1-4: Plants yielding special products of economic importance: 

 fibers, oils, latex, drugs, beverages. Autotetraploids increased the size 

 of seed, fruit, leaf, stem, and root, and larger plant organs should 

 yield more substances of economic importance.--^" Oil-bearing seeds 

 such as sesame, Brassica, and flax, all have lower seed production as 

 tetraploids. Flax is a notable case where the fertility drops extremely 

 low. Rubber increase in Koh saghyz and Hevea are objectives. Fiber 

 improvements in Hibiscus, cotton, flax, jute, and hemp have been 

 sought via polyi^loidy. Anabasine in polyploid Nicotiana increased 

 with polyjiloidy. 



13.2: Triploidy 



Hybrids from a tetraploid seed parent crossed with a diploid 

 pollinator are triploid. As such these are not stable, and both male 

 and female gametes are sterile from unbalanced chromosomal dis- 

 tributions. The vegetative vigor is not lowered, in fact many triploids 

 are extremely vigorous. Among the good varieties of apples, triploids 

 are common. In nature some triploid species are widely distributed. 

 Polygouatuin rnultiflorufn is an example of a triploid having a range 

 from the northwestern Himalayas throughout Eurojje. 



The two kinds of triploids are the autotriploid and allotriploid. 

 The former arises from an autotetraploid crossed back to the parental 

 diploid, whereas the allotriploids involve two species. In these cases 

 bivalents and univalents are found at meiosis. Triploids offer the 

 opportunity for increasing the frequency of aneuploids since the trip- 

 loid female gametes are viable with one or two chromosomes above 



