1928] HoUingshead : Chromosomal Chimeras in Crepis 349 



young embryo which gave rise to the growing point of the stem. 

 Nawaschin was led to favor this theory of the origin of tetraploids by 

 the frequency of 4)1 plants in Crepis tectorum. He calculated the fre- 

 quency of diploid gametes from the number of triploid plants obtained 

 in over 4,000 individuals, and on this basis determined the number of 

 tetraploids which should occur by chance meeting of those gametes. 

 He found the expected number of tetraploids to be much less than that 

 actually occurring. He concluded, therefore, that tetraploids arose 

 through the doubling of chromosomes in the fertilized egg cells. 



In view of the increasing number of cases in which tetraploidy has 

 arisen in normal diploid tissue, one is justified in concluding that it 

 may play a part in the origin of polyploid species and interspecific 

 hybrids. 



I acknowledge with pleasure my indebtedness to Dr. J. L. Collins 

 and Professor E. B. Babcock for the material used in this study. 



SUMMARY 



Tetraploidy was observed in the roots of two different plants. One, 

 a C. biennis x C. setosa hybrid derivative, had one root partly tetra- 

 ploid. The other, a plant of C. Bureniana, had two roots wholly 

 tetraploid. 



No external factors could be associated with the tetraploidy. 



Giant multinucleate vacuolated cells occurred in another root of 

 the same C. Bureniana plant. Evidence of cell and nuclear fusion was 

 observed. It is doubtful whether this phenomenon has any significance 

 in relation to the origin of the tetraploid roots. 



Tetraploidy arising in somatic tissue probably plays a part in the 

 origin of polyploid species and interspecific hybrids. 



