8 THE QUANTITATIVE METHOD IN BIOLOGY 



original form. We may, for instance, look upon the trans- 

 formation of blue flax into white flax (or vice versa), of 

 Solanum nigrum with black fruits into Sol. nigr. with green 

 fruits, etc., as being the result of a qualitative transformation 

 of the living mixture with regard to one of its components. 



We may also imagine two, three or more components to be 

 simultaneously transformed, the consequence of which woiild 

 be the appearance by saltation (mutation) of a new species 

 quite different from the original one, and even of a new genus, 

 a new family. (See bud-variation, § 20.) ^ 



§ 9.— MUTATION. LAMARCK ISM. —Among the possible 

 causes of mutation alluded to in § 8a, the influence of external 

 factors deserves a special mention. (See §§ 35 and 105.) 



A change in the conditions of life of certain specimens of a 

 species may result directly in a mutation. 



It is also conceivable that a quantitative modification of a 

 living mixture produced by external causes may become im- 

 portant enough to bring about indirectly a qualitative modifica- 

 tion — i.e. a mutation. We know that the reactions which take 

 place in a mixture of chemical entities depend, in certain cases 

 and to a certain degree, on the proportions in which the entities 

 are mixed. Therefore it is conceivable that a change in the 

 proportions of a living mixture (quantitative modification) 

 might produce a new reaction resulting in a mutation. 



If we adopt the suggestion that mutations may be brought 

 about, directly or indirectly, by external causes, there is no 

 longer any incompatibility between 



The principle of mutation {saltation), according to which a 

 new species may appear at once, and 



The Lamarckian principle, according to which new species 

 are produced by new conditions of existence.^ 



Both principles being combined, ^ the transformation of a 

 species into a new one, without transitory or transitional forms 

 between both, becomes quite intelligible. 



» According to the above a fundamental distinction ought to be made 

 between two kinds of heredity : 



(a) The hereditary transmission of quantitative modifications of the living 

 mixture of a species ; by this, no new species can be produced. 



(6) The hereditary transmission of qualitative modifications of the living 

 mixture of a species ; this gives birth to a new species. 



2 Without selection. 



' That is to say, the production of mutations by external causes being 

 admitted. 



