The Aneuploids 355 



demonstrated cytologital evidence that this plant and others lound 

 between 1915 and 1920 each contained a single extra chromosome. 

 In 1938, a summary covering 60,000 field-grown ofFsj^ring from types 

 with extra chromosomes was published.'' The term trisornic, as the 

 extra chromosomal j^lant was called, is used in cytogenetics. 



With the use of colchicine in polyploidy and in Beta there arose 

 an opportunity to study the effect of chromosomal variation in sugar 

 beets. •'"^* It is one of the most intensively studied species as well as 

 one of great practical importance in many coinitries. The large- 

 scale ])roduction of tetraploids in 1938 with subsequent triploids 

 opened opportimity to study variation in regard to chromosomal 

 numbers. Since trijjloidy was discussed in the chapter on autoploidy, 

 that will not be repeated. Here the influence of separate chromo- 

 somes, the trisomies, are of special consideration.''" 



Progenies from triploids intercrossed, and backcrossed to diploids, 

 included plants with chromosomal numbers from diploid to tetra- 

 ploid and beyond. One or more plants ranged from 18 to 36 chromo- 

 somes. ^o Between 37 and 45 several classes were missing. This 

 material arose from colchicine-treatcd seed of the Hilleshog strain at 

 Svalof, Sweden. When the seed j^arent was a triploid and the pollen 

 parent diploid, all numbers from 2x to 3x were recovered. A recipro- 

 cal cross yielded an excess of diploids (77 per cent) with classes from 

 21 to 25 missing. The transmission difference between seed and 

 parent confirms what had been learned long ago. Extensive pollen 

 tube studies by J. T. Ruchhol? demonstrated the effect of extra 

 chromosomes in Datura upon the male gametophyte. 



Effects of different chromosomal classes upon a whole series of 

 morjihological and physiological characters in sugar beet were com- 

 pared. Since this study permitted analysis of the entire population, 

 certain advantages Avere presented that had never been jjossible be- 

 fore this time. Every chromosomal class from 18 to 36, inclusive, was 

 analyzed as follows: (1) field estimation, (2) weight of tips and roots, 

 (3) refractometer determinations, and (4) leaf development. The 

 trisomies were distinct in plant characteristics, and the particular 

 chromosome stamped its influence on growth habit. An interesting 

 problem that requires more attention is the possible correlation be- 

 tween vigor increase and decrease in the size of the extra chromosome. 

 This point becomes important when transfer of characteristics by 

 single chromosomes is attempted. In addition to single trisomies, two 

 plants with 20 chromosomes were studied. Plants beyond the 36 

 chromosomes, including a 42-chromosomc plant, had good \igor. 

 Finally the optimal niunbers as would be predicted have three modes; 

 these are diploid, triploid, and tetrajiloid. Maximum viability occurs 

 at the euploid number.'"* 



