E. MUTATIONS 

 Lecture XVI 



THE ORIGIN OF THE PELORIC TOAD-FLAX 



I have tried to show previously that species, in 

 the ordinarv sense of the word, consist of dis- 

 tinct groups of units. In systematic works 

 these groups are all designated by the name of 

 varieties, but it is usually granted that the 

 units of the system are not always of the same 

 value. Hence we have distinguished between 

 elementary species and varieties proper. The 

 first are combined into species whose common 

 original type is now lost or unknown, and from 

 their characters is derived an hypothetical im- 

 age of what the common ancestor is supposed 

 to have been. The varieties proper are derived 

 in most cases from still existing types, and 

 therefore are subjoined to them. A closer in- 

 vestigation has shown that this derivation is 

 ordinarily produced by the loss of some definite 

 attribute, or by the re-acquisition of an appar- 



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