;;,St) Lutz, Triploid Mutants in Oenntlierfi. 



cultures of Oenothera. He called attention to the fact that no 

 offspring had been grown from the two last plants of de Vries' 

 culture which had been identified as 0. gigas, and it was therefore 

 possible that they were triploid, and not tetraploid mutants. He 

 also stated that he agreed with Professor de Vries in the opinion 

 that such ,,halve mutanten" have since been repeatedly derived 

 from seeds of purely fertitized 0. Laniarrkiana. 



Recently (1911), in referring to Stomps' (21) statements in 

 regard to the possible origin of the tetraploid condition in 0. gigas 

 through the union of two mutated" germ cells which had 14 chro- 

 mosomes each, Gates says (15): 



"If Stomps' theory were correct, we should have a mutant 

 occurring with twenty-one chromosomes, and it would be much 

 more frequent in occurrence than in 0. gigas. Such a mutant has 

 never yet been found, and all the other mutants which are known 

 have fourteen chromosomes, as in 0. Lamarckiana" 



It is not the purpose of this paper to discuss the manner in 

 which 0. gigas arose. Such evidence as has been observed in the 

 somatic cells of Oenothera. bearing directly upon this subject will be 

 fully stated and discussed in more detailed reports to follow. In view, 

 however, of the above assertions by Gates and Stomps, it was 

 thought desirable to oft'er some statement in advance concerning the 

 appearance of a 21- and a 22-chromosome mutant among the pedigreed 

 cultures of Oenothera at the Station for Experimental Evolution 2 ). 



In the summer of 1908, I recognized a new form (Fig. 3) 3 ) 

 among the Lamarckiana hybrid offspring of 0. lata X O. Lamarckiana 

 which was found, from studies of root-tips in 1909, to have 

 21 chromosomes (Fig. 1). Two individuals were observed in sepa- 

 rate cultures of this cross. A close watch was kept for the re- 

 appearance of this form in 1909, but it was not recognized 4 ). It 



2) All the Cold Spring Harbor cultures to which I shall refer in this or suc- 

 ceeding papers may be understood to have descended through pedigreed cultures 

 of guarded pollinations from plants or seeds from de Vries unless clearly stated 

 to the contrary. Most of the somatic counts referred to in this paper were determined 

 from sections of root-tips, but a few were obtained from sections of young buds. 

 None were considered established unless clearly demonstrated beyond all possible 

 question. In most cases these were determined from a large number of figures 

 in metaphase distributed through 3 or more fixations from each plant. 



3) This photograph is unfortunately very poor, but it will serve to illustrate 

 several of the chief points of interest in connection with this mutant. 



4) A culture of 0. nanella X 0. gigas was grown in the summer of 1909, 

 and -40 offspring came to flower as annuals, a large number of which strongly 

 resembled the offspring of 0. Lamarckiana X 0. gigas growing in the garden at 

 the time. Two individuals, however, had many points in common with the 21-chro- 

 mosomc mutant. Somatic chromosomes of one of the two were studied and the 

 number found to be in the region of 21, and probably 21. Inasmuch as this is 



