384 University of California Publications in Agricultural Sciences [Vol. 2 



found to occur spontaneously in cultures of Oenothera Lamarkiana, 

 its orient still remains somewhat obscure. Based on the observations 

 of B. Nemec (1910) and Ishikawa (1918) on Gagea and Oenothera, 

 R. Gates (1924) suggested that dispermy should be responsible for 

 triploidy. The majority, however, are inclined to accept the same 

 manner of origin as in experimental triploids, viz., occurrence of 

 diploid gametes. The third conceivable explanation, viz., formation 

 of the embryo from a cell of the endosperm, remains purely specu- 

 lative since such a phenomenon has never been observed in any plant. 



In the case of Crepis the writer does not hesitate to suggest the 

 first method, for several spontaneous "triploid" hybrids have been 

 found which have arisen through the open pollination of diploid 

 plants of C. capiUaris (Navashin, 1927). It is obvious that such 

 interspecific hybrids could not obtain a diploid capiUaris complex 

 except from a diploid egg cell ; it is quite improbable that two sperms, 

 one belonging to C. capiUaris and the other to another species, could 

 fertilize a normal egg, and thus give rise to a triploid hybrid. 



The occurrence of occasional functional diploid egg cells being 

 clear enough, the question arises as to the influence of the increased 

 chromosome number on the sexual function of the female gamete. 

 R. Gates {he. cit.) on the basis of the data on apogamous plants 

 doubts the very possibility of fertilization of a diploid egg, the latter 

 circumstance being, he thinks, an indirect proof of his hypothesis of 

 dispermy. It has been showai, however, that diploid eggs are capable 

 of fertilization as well as haploid ones ; and moreover, it has been 

 possible to demonstrate that not only diploidy but even higher grades 

 of polyploidy do not affect the sexuality of the gamete. Pollinating 

 triploid capiUaris (after the usual castration) with the pollen of 

 other Crepis species usually gave triploid hybrids, but, as shown 

 above, a few plants possessing more than two haploid capiUaris 

 chromosome complexes were obtained. As a result of crossing two 

 triploid plants together, not only triploid and tetraploid but also 

 pentai)loid plants were obtained. Finally, as has been shown in table 

 •'3, a heptaploid (7n) plant of C. capiUaris was found in the immediate 

 progeny of a triploid. 



From these results it is evident that besides diploid egg cells 

 triploid, tetraploid, and i)ossibly even pentaploid or hexaploid ones 

 are formed, and that these polyploid egg cells undergo normal fertil- 

 ization, producing zygotes possessing as highly multiplied chromo- 

 some complexes as 7n, i.e., twenty-one chromosomes in.stead of the 



