

CHROMOSOMAL CHIMERAS IN CREPIS 



BY 



LILLIAN HOLLINGSHEAD 



Gates (1924) stated that "it is unknown at the present time how 

 widespread polyploidy in somatic tissues may be." Several writers 

 have since that time reported cases of somatic polyploidy and it was 

 thought worth while to put on record instances of this condition 

 recently discovered in the Genetics Laboratory of the University of 

 California. 



In the course of an examination of root tips of various Crepis 

 species and species hybrids, two plants which were partly tetraploid 

 have been found. ^ These are not the first cases of chromosomal chi- 

 meras reported in Crepis, Lesley (1925) and Nawaschin (1926) having 

 previously recorded the phenomenon. Lesley 's report is a note stating 

 that in an F^ between C. hiennds (71 = 20) and C: faetida {n:^5) 

 a few neighboring cells were found having about twice 25 chromo- 

 somes, whereas most of the cells contained the expected 25. Nawaschin 

 reported the occurrence of a tetraploid area in the form of a narrow 

 sector in a diploid root of C. Dioscoridis (^ = 4). 



The first of the two cases to be described was that of a chimeral 

 root of a derivative from a cross between Crepis biennis (71 = 20) and 

 C. setosa (w = 4) which had 24 chromosomes in most of the somatic 

 cells. In this root, however, a large number of cells was found which 

 obviously had many more than the normal 24 chromosomes, several 

 approximated 48, and two cells gave clear accounts of 48 chromosomes. 

 The normal and tetraploid chromosome complexes are shown in 

 figure A. By an examination of successive sections it was determined 

 that the tetraploid cells were confined to a definite region which 

 extended from at least very close to the root cap to a point where no 

 division figures could be found. Apparently the longitudinal outlines 

 of the tetraploid area were fairly regular, since only one case occurred 

 in which diploid and tetraploid cells were found in different sections 

 occupying the same position relative to the circumference, and this 

 was on the line of demarcation between the two areas. 



1 Since writing the above a root of C. Hnkelei (n^=8) containing several 

 neighboring cells with about twice the normal chromosome number and one of 

 C. mon.taiia (}i, = 6) with one tetraploid cell have been found. 



