Lutz, Triploicl Mutants in Oenothera. 403 



the poles, and that the divisions are regular as described by G ates for 

 a 21-chromosome plant, with only an occasional exception (such as he 

 has noted in this form) of one chromosome passing to the wrong pole. If 

 all remain normal, we should then have germ cells resulting as Gates 

 has indicated, with 10 and 11 chromosomes commonly, and 9 and 

 12 exceptionally. These may so combine as to produce commonly, 

 offspring with 20, 21 and 22 chromosomes respectively; and offspring 

 with 18, 19, 23 and 24 chromosomes respectively, occasionally 

 (provided of course that functional germ cells may result from an 

 irregular distribution of chromosomes). According to expectations, 

 21-chromosome plants should occur most frequently among these 

 offspring, and 18- and 24-chromosome plants most rarely. It does 

 not necessarily follow that each of the former should duplicate the 

 vegetative characters of the 21-chromosome parent, nor that all of 

 these offspring should conform to one type. 



If we assume that chromosome numbers much in excess of that 

 of 0. Lamarckiana are always associated with vegetative characters 

 which suggest certain vegetative characters of 0. yigas more or less, 

 the above numbers (18, 19, 20, 21, 22, 23 and 24) would be suf- 

 ficient to account for most of the offspring of the 21-chromo- 

 some mutants which were recorded as having vegetative char- 

 acters resembling O. yigas more or less; but they could not 

 account for the large number of Lamarckianas among the offspring 

 of one of these mutants. Neither would Geerts' observations alone 

 explain the presence of certain gigas-\ike characters in others, 

 unless, as he states (16, p. 163) for the second generation offspring 

 of 0. gigas X 0. Lamarckiana, a 14-chromosome offspring of a 

 21-chromosome plant may resemble 0. yigas as strongly as did the 

 parent. 



If, however, we consider the possibility of irregularities of the 

 second type observed by Gates and Davis (in which one or more 

 apparently normal chromosomes fail to be included within either 

 daughter-nucleus at the heterotypic or homotypic division of the germ 

 cells), then we might easily complete the series from 24 to 14. However, 

 it would be surprising to find that this last irregularity is of sufficiently 

 common occurrence for a self-pollinated 21-chromosome plant (5483) 

 to produce over 70 fourteen-chromosome offspring in a total of 77. 

 If these Lamarckiana offspring had each 14 chromosomes, as we 

 may assume with a fair degree of certainty, I think it is probable 

 that this number was derived in each case from the fertilization of 

 a 7-chromosome egg by a 7-chromosome sperm, and that these 

 germ cells were produced in the manner described by Geerts. 



On the basis of the nature of the vegetative characters of the 

 offspring of the Cold Spring Harbor 21-chromosome mutants, the 

 following suggestions may be offered as working hypotheses: 



26* 



