THE EVOLUTION OF LIVING BEINGS. 31 



Mendelism deals with the behaviour of gametes already 

 formed. 



As such however, it can be of service, because, al- 

 though it is unable to show us how the change necessa- 

 ry to bring about the heterozygous condition, took 

 place, it can show us the result viz : the then heterozy- 

 gous condition of the previously homozygous orga- 

 nism. 



If we now define a mutation as the change of consti- 

 tution, undergone by a homozygous individual which be- 

 came heterozygous without having been crossed, we can 

 say, that proof of mutation would be at hand, if 



IT WERE SHOWN THAT A HOMOZYGOUS INDIVIDUAL CAN ^ 

 BECOME HETEROZYGOUS WHEN ALL POSSIBILITY OF A 

 CROSS IS EXCLUDED. 



Mendelism could show us, that such mutation had 

 taken place, if we were but sure — it is the old diffi- 

 culty again — of the homozygous condition, e. g. of the 

 specific purity of the material from which the supposed 

 mutants arose. Does the classic subject for mutation: 

 Oenothera Lamarckiana give us proof for the existence 

 of such mutations? 



The answer is an unconditional:, no. 



In the first place, Oenothera Lamarckiana has never 

 been obtained as yet, in a homozygous condition e. g. 

 in a condition that it threw no „mutants"; every La- 

 marckiana-individual, so far examined, „mutates", was 

 consequently impure already, so that the bringing to 

 light of these mutants was comparable to the bringing 

 to light of the presence of silver in a lead-ore contai- 

 ning silver. 



