Lutz, Triploid Mutants in Oenothcru. 



5. The completion of the reduction division in the normal 

 manner, or irregularly, according to 1 or 2. The subsequent arrest of 

 the homotypic mitosis (in the cell destined to differentiate the 

 embryo sac) before the division of the nucleus has taken place, 

 resulting in the production of a functional germ cell with a chro- 

 mosome number double that of its reduced number. 



This is assumed by Professor Gregoire to be a much less prob- 

 able explanation of the origin of mutant somatic chromosome number 

 in Oenothem than the irregularities of the heterotypic mitosis, 

 and is supposed under any circumstances to be of much more rare 

 occurrence than the latter. However, since so many of the numbers 

 in question can be explained on this basis alone, and still more 

 when we consider this in connection with the simple irregularities 

 of chromosome distribution observed in the heterotypic mitosis of 

 the male germ cells, we can not ignore it as a possibility until 

 we have evidence to discredit it. 



The w T orks of Strasburger and others upon various species 

 of plants have demonstrated that reduction division may be arrested 

 at any stage of the heterotypic prophase. and even at the metaphase. 

 Professor Gregoire believes that it is not improbable, therefore, that 

 this phenomenon may occasionally extend even further in Oeno- 

 Htcra and result in the failure of a dyadocyte to complete the 

 homotypic mitosis. 



The maturation process in Oenothera is, properly speaking, 

 a continuous one from the beginning of the heterotypic prophase 

 to the completion of the homotypic division. The figures of Davis 

 for 0. Lainan-kifutn and 0. yiyas (4, Figs. 30 and 67) clearly show 

 that the chromosomes sometimes split as early as the middle and 

 late anaphase of the heterotypic mitosis in preparation for the 

 homotypic division, while Gates (7, p. 95) found that this fission 

 sometimes appeared as early as the late metaphase of the hetero- 

 typic mitosis in the "Lawarr-kidna hybrid". There is furthermore 

 no true resting stage between the heterotypic and homotypic divis- 

 ions of this group of plants. Gates states with reference to 0. 

 nthrincrris (11, p. 17) that 'the nuclei never pass into the resting 

 condition and the chromosomes never loose their identity completely, 

 though they spread out and anastomose with each other more or 

 less.' He also states that in 0. yigas (12, p. 528) 'the chromosomes 

 may stretch out and anastomose with each other', passing into what 

 he terms a 'semi-resting condition'. Davis found that during 

 interkinesis in O. bicnnis (3, pp. 638 039) 'the free ends of the 

 chromosomes sometimes exhibit a tendency to branch and become 

 united to form a loose and imperfect network', and adds "but 

 generally most of the chromosome pairs of a nucleus are as clearly 

 defined as in Figs. 29 and 30. ... It is clear that the chromo- 



