r 



LIXXEAN SOtlEXr Of LOXDOX. 



91 



merel)' lost an inhibitor for six toes, wliieh all its uiirortuiiate 

 ancestors all the way back to Amoeba possessed, but could not get 

 rid ot I 



Any such view of evolution founded only npon the cases oE 

 negative mutations is sufficiently bizarre, but Dr. Lotsy would 

 deny us even this ! However, I think we may not only agree 

 ,witli the Mendelians that negative mutations through the loss of 

 iunit-characters do frequently occur ; but we can, moreover, con- 

 fidently assert that mutations of a divergent and positive kind 

 occur as well. 



Referring now to the CEnotheras, my view has been that tlie 

 'species Ct\ Lani'irchiana is in a condition of germinal instability, 

 leading to various types of germinal change in certain of the 

 oifspriug. The cause of this condition, whether from crossing, 

 [change of climate, or other agencies, is immaterial to the present 

 [argument. The nature of some of these changes has been clearly 

 demonstrated by the cytological work of others and myself ; and 

 jl challenge Dr. Lotsy to offer an explanation of the origin of 

 (E. mut. lata and CE. mut. i/igas on the basis of this theory, which 

 is at the same time in harmony with the cytological facts. I 

 should be glad if Professor Eateson woiild also answer this 

 :question in terms of factors. 



Dr. Lotsy says the fundamental point is whether the mutants 

 owe their origin to the addition of a new factor to ffi". La- 

 \marckiana .'" But I deny that the fundamental point is anything 

 of the kind. The crucial point is whether an inherited germinal 

 change, i.e. a mutation, has taken place. The behaviour of the 

 ichromosomes shows with certainty the nature of the visible 

 change which has occurred in the two cases I have cited. In 

 \gigas the chromosomes have changed from 14 to 28. In lata 

 tthey have changed from 14 to 15. I challenge Dr. Lotsy to pro- 

 duce an explanation on his theory which will show that the same 

 [kind of change occurred in both these mutations. 



Six years ago I was able to show that during the reduction 

 [divisions in (Fnothera, both members of one pair of chromosomes 

 i occasionally go into the same germ nucleus. This is how lata 

 originates, and Miss JS'esta Thomas and myself have recently 

 shown that lata, no matter from what source, invariably has 

 15 chromosomes. Lata does not therefore possess a new unit- 

 factor, but a duphcate for one of its pairs of chromosomes, and 

 |the essential germinal change or mutation occurred in the reduc- 

 Ition division which resulted in a germ-cell having 8 chromosomes. 

 This process is directly contrasted with the regular Mendelian 

 recombinations of characters. If this does not satisfy Dr. Lotsy 

 as a germinal change, then nothing but a special creation of a new 

 unit-character would satisfy him. I have found the same cyto- 

 logical change occurring in the wild ffl". biennis in America, which 

 is regularly self-pollinating. 



Again, in (E. gigas we have an experimentally demonstrated 

 case of the sudden origin of tetraploidy, i. e., the 4.v number of 



