1929] Navashin: Triploidy in Crepis 383 



relatively small number of diploids and triploids occurred. In C. 

 dioscoridis the diploid plants predominate, and trisomies occur only 

 in small numbers, approximately equal to the number of triploid 

 plants. 



In addition to trisomies and other variations resulting from 

 numeric changes of whole chromosomes among the progeny of triploid 

 plants, cases were found of alterations in the chromosomes them- 

 selves. Thus in C. capillaris one plant was found to possess a frag- 

 mented D-chromosome. This particular plant possessed a very small 

 satellited chromosome (r/), representing the proximal part of the 

 normal satellited chromosome, which behaved as a new' autonomous 

 chromosome. Similar fragmentation of the satellited chromosome has 

 been found to occur in the progeny of triploids in C. tectonim. In 

 the latter species several other alterations in chromosome organiza- 

 tion have also been observed (1926). One case of fragmentation is 

 illustrated in plate 57/. 



Finally, several spontaneous interspecific hybrids have been found 

 in the progeny of triploid plants. The majority of them possessed 

 two haploid complexes of one species and one of the other ; but a 

 few were also found which possessed three haploid sets of one species 

 and one of the other. 



DISCUSSION AND CONCLUSIONS 



The manner of origin of the original triploid C. capillaris plant 

 ("194:7") could not be finally established. Since triploidy. in con- 

 trast to tetraploidy, cannot be a consequence of a purely vegetative 

 process, the "summation" of three haploid chromosome complexes 

 in a zygote should theoretically be due to one of the following causes : 

 viz., (1) formation of a diploid gamete followed by fusion with a 

 normal haploid one; (2) dispermy; and (3) formation of an embryo 

 from a cell of the endosperm. 



In all the triploid individuals known to have arisen under experi- 

 mental conditions the manner of origin has been proved only in the 

 cases of triploid Oenotheras and Daturas, the plants being obtained 

 artificially from crosses of tetraploids with diploids (Geerths, 1911; 

 Blakeslee, 1924). There is no doubt, consequently, that in these 

 particular instances triploidy is due to fusion of a diploid gamete 

 with a haploid one. As for the other well-known instance of triploidy 



