1^0. 6i2] 



r ABLATION IN DATURA 



25 



lation, but from other parents the whites wwr ;ii)])roxi- 

 mately 6 times as frequent as would be cxprcicd. Later 

 experiments seem to indicate: tliat w(^ i;'et tlie detinite 

 excess in white offs])riii.i;' fi'om sinii)K x parents when both 

 the "white " chromosomes conic from the German hne; 

 that we get the P(dnscttia ratios ty])ical of random as- 

 sortment when the two white ehroniosomes come from the 

 Washiiiii'toii whites : and that wo ,<;vt both of the two types 

 of i'atio> from dirfoi-ent iiidi\i(hial I-', parents when we 

 make n|) an \'\ 1 *oiiiscttia eontainin.u' hoih a Washington 

 wliite. an<! a (iei'mau white elii-omosonie. it is apparent 

 that the pecnliai'ity mnsi b,. attributed to the derman 

 chromoximes. Tile (luestioii is I'cceiving further experi- 

 mental investigation l)ut our provisional hypothesis to 

 account for the dititerencc in the ratios is that for some 

 reason in trisomic disjunction the German white chromo- 

 somes go to opposite poles rather than to the same pole 

 6 times as fre(piently as the laws of random assortment 



T.et us retui-n to oui" diagrams in Fig. 1*. Of the modi- 

 fied di])]oids we nia\- ha\-e - extra chromosomes in a 

 sinule set forniim;' a simple mutant of the formula 

 (i';/-L'). An examph. is the round-leaf Globe (fig. 1) 



If two (HtTcrent sets are affected each with a single 

 extra clii'oniosonn^ we liavc a do\d)h- mutant with the 

 formula ( L';/ -f 1 4- 1 ' • < 'f thi' (ili ditVereiit .h)uble tri- 

 somic mutants thoretically i)os>ii.le, we liave a consider- 

 able number now under cuhivati(Ui. As an example, the 

 double mutant ( ih.].e-b*e,hn-ed is shown in Fig. G. At the 

 top is a cai)srdc of a n(»rnial (riph)id witli its chromosomal 

 diagram. At the hd't is a cap>uh' of the (ih)l)e. and at the 

 right a eapside of iJeduceiL Their diagrams indicate that 

 the two mutants have (iitb rent sets affected. Th(^ plant 

 re])r(>scnted by the capsuh's heh)w. fi-om the appearance 

 of it^ leaver 'a> well a> fi-.>m that of it^ fruit. i>« un- 

 doubtedlv a <loublc mutant with the two s.'t^ aibctcl as 

 indicat.'d in the diagram below. If the ( I lo])e-h'educed 

 behaves like other d.nd.h- mutants we have bred, its oft- 



