No. 638] 



TYPES OF MUTATIONS 



255 



Naudin (9) and Godroii (7) as well as the later investi- 

 gations of deVries (13), Bateson and Saunders (1) and 

 the writer and Avery (4) on this species have shown that 

 purple color in flower and stem is doniiiiaiit to lack of 

 purple in those parts, and that spiny eapsiih's air dom- 

 inant to smooth capsules. The writei- wiih A very lo) 

 has been able to add a third pair of contrasting- char- 

 acters: "many nodes," causing tall stature, in contrast 

 to "few nodes," causing low stature. These are all the 

 allelomorphic pairs actually determined. Moreover, no 

 variation has arisen in the writer's cultures during the 

 last seven years' study of this species which gave evi- 

 dence of differing from the present stock by a single 

 Mendelian factor. Distinct variations, provisionally 

 termed mutations, have, however, regularly recurred 

 whenever a sufficiently large number of plants have been 

 subjected to observation (5). So far as investigated, 

 they have been found to be connected with a duplication 

 of one or more of the normal chromosomes (6). The 

 normal quota is 12 pairs : 12 being therefore the gametic, 

 haploid, or x number; and 24 the somatic, diploid, or 

 2x nnml)er. Tlic simplest type of diii)Iieation is the ad- 

 dition of an extra chroniosoHn-. i)i-ol)al)l\- by non-disjunc- 

 tion in one of the ])airs of the dijjloid coni])lenient, giving 

 24 + 1, or 25 chromosomes as the somatic number. In 

 such plants there will be 11 sets of 2 homologous chro- 

 mosomes each and 1 set of 3 homologous chromosomes. 



We have on the chart, Table I, 12 recurrent mutants 

 of the type just discussed; which, while jun-fectlv dis- 

 tinct from each other and from the nornnil sToek. have 

 certain characteristics in eonnnon. All lia\e heen found 

 to produce gametes with 12 ati/l l.'l chromosomes (there- 

 fore with 20 as the calculated somatic number) : all have 



ing in the different mutants fvom S per cent, in the 

 Globe to 21 ])ei- (-.■nt. in the Spinach, as imlieate.l in the 

 chart: all fail to transmit the mutant con.iHex to any 

 consi.lerable extent throu-h tin- p.>llen. while tln-v do 



