No. 443] MUTATION IN PLANTS. 743 



to the parent type, and their constancy or fixity might not be 

 increased by artificial selection. 



7. More than one mutant might arise simultaneously from 

 the parent individuals. 



8. Any one of the several mutants observed might originate 

 from several parent individuals simultaneously. 



9. The mutant forms might arise from successive genera- 

 tions of the parent types. 



10. The mutant forms might in turn give rise to new types 

 after their separation from the parent type. 



The above statements rest directly upon observations of care- 

 fully conducted experimental cultures and admit of but little 

 argument as to interpretation. With this positive evidence at 

 hand questions at once arise as to the frequency, occurrence, 

 prevalence, e.xclusiveness, and as to the mechanism of discon- 

 tinuous variation as a method of origin of new species. When 

 we take up these points we at once enter a field of speculation 

 in which it may be seen there is opportunity for unlimited 

 argument, and in which with the bias to which most of us are 

 subject as a result of our training and investigations, it is diffi- 

 cult to maintain a purely judicial attitude. It will be profitable 

 to recall some of the more important facts bearing upon these 

 matters however. 



First, as to the occurrence of discontinuous variations in plants 

 the following examples cited by Korschinsky will be illustrative : 

 Erjthriua crista gain \\2i^'mXxod\xcQQ[ into cultivation in 1771 and 

 no aberrant forms were seen until seventy-three years later: Bego- 

 nia sevipcrflorcns showed deviating forms only after fifty years : 

 Cyclamen persicnni gave no unusual forms until after one hun- 

 dred and twenty years of observation : no mutations were 

 obser\'ed in Ipomoea purpurea in one hundred and twenty years. 



De Vries observed many thousands of individuals of a hundred 

 species growing in the vicinity of Amsterdam in 1886 and 1887 

 and found mutations in only one, that one Ginothera laniarck- 

 iana. He points out that remains of plants of various species 

 found in mummy cases four thousand years old have been found 

 identical with living species in all recognizable characters. As 

 a result of a rough examination he also concludes that the 



