ORIGIN OF MUTANT CHARACTERS 71 



duced the mutant gene but rather its release from its 

 lethal linkage. 2 



It seems, then, that the mutation process in Lamarck's 

 primrose is probably not essentially different from famil- 

 iar processes that occur in other plants and animals. In 

 other words, there are no longer grounds for interpreting 

 the mutation process that it shows as differing essentially 

 from what takes place in other animals and plants, except 

 that some of its recessive mutant genes are concealed, 

 owing to the presence of lethal genes. 



These considerations remove, I think, any necessity for 

 assuming that a new gene is added, even when a new or 

 progressive type of Oenothera appears. It may be that 

 such progressive types as de Vries had in mind arise 

 through the accidental addition of a whole chromosome to 

 the normal set. This question will be considered in Chap- 

 ter XII, but it may be said here that there is very little 

 evidence that new species can often be produced in this 

 way. 



2 Shull has interpreted the appearance of a number of the recessive types 

 of O. Lamar cTciane, on the lethal-linkage hypothesis. S. H. Emerson has re- 

 cently pointed out that Shull's evidence, so far published, is not entirely 

 cogent, but it may, nevertheless, be valid. De Vries himself, in recent pub- 

 lications, seems not averse to accepting the lethal interpretation for certain 

 of the oft-repeated recessive mutants that he places in the "central chromo- 

 some. ' ' 



