1929] Navashin: Triploidy in Crepis 385 



normal diploid number, six. How far increase in chromosome 

 material may go in Crepis is still unknown. 



These curious results clearly demonstrate once more that increase of 

 chromatin material of itself cannot produce development of the zygote 

 because the diploid, triploid, tetraploid, and perhaps pentaploid or 

 hexaploid eggs are normally incapable of development without fer- 

 tilization. Apparently the male gamete contributes some stimulating 

 materials besides the usual chromatin materials. Thus direct cyto- 

 logical study supports once more Loeb's famous conclusions. 



We may conclude, therefore, that triploidy in Crepis is due to the 

 occasional formation of diploid gametes, probably of the female ones. 

 There is a possibility, however, that an occasional diploid pollen 

 grain may function, although it has not been certainly demonstrated. 



As to the manner of origin of diploid gametes three possibilities 

 may be suggested, viz.: (1) omission of the reduction division; (2) 

 duplication of the reduced (haploid) nucleus; and (3) formation 

 of tetraploid groups of somatic cells followed by normal reduction 

 during sporogenesis in the resulting tetraploid tissues. 



The data presented here being insutficient to arrive at a definite 

 conclusion, one may equally suggest any one of these three conceivable 

 ways, inasmuch as all of them are known to take place. Omission of 

 the reduction division, particularly under the influence of various 

 chemical and physical factors, is a well-known phenomenon; forma- 

 tion of groups of tetraploid cells, besides other numerous instances, 

 has also been found in Crepis (M. Navashin, 1926; Hollingshead, 

 1928a) ; and duplication of the haploid nucleus in the female gameto- 

 phyte has been recently confirmed bj^ Newton (1927). 



It is interesting to point out that cytology provides a unique 

 method of demonstrating the mode of origin of a diploid gamete when 

 other methods fail or for some reason are inapplicable. If the homo- 

 logous chromosomes in the same nucleus possess distinguishing 

 features one may directly arrive at a definite conclusion as to the 

 derivation of the diploidy of the gametes, and consequently of the 

 triploidy. Advantage may be taken of the occurrence of size differ- 

 ences of the satellites of homologous chromosomes, such as have been 

 demonstrated above. If the original plant possesses unequal satellites 

 the occasional diploid gametes produced by it will be different accord- 

 ing to their mode of origin. Thus if diploid gametes are produced 

 by non-reduction they will uniformly contain a pair of unequal satel- 

 lites. On the other hand, if diploid gametes are formed as a result 



