276 SIGNIFICANCE OF SEXUAL REPRODUCTION [V. 



is not inherited, and cannot be transmitted : it disappears with 

 the organism which manifests it. Not only do similar pheno- 

 mena occur in the vegetable kingdom, but they present them- 

 selves in an especially striking manner. 



When Nageli^ introduced Alpine plants, taken from their 

 natural habitat, into the botanical garden at Munich, many of 

 the species were so greatly altered that they could hardly be 

 recognized : for instance, the small Alpine hawk-weeds became 

 large and thickly branching, and they blossomed freely. But 

 if such plants, or even their descendants, were removed to a 

 poor gravelly soil the new characters entirety disappeared, and 

 the plants were re-transformed into the original Alpine form. 

 The re-transformation was always complete, even when the 

 species had been cultivated in rich garden soil for several 

 generations. 



Similar experiments with identical results were made twenty 

 years ago by Alexis Jordan ^, who chiefly made use of Draba 

 verna in his researches. These experiments furnish ver}^ 

 strong proofs, because they were originally undertaken without 

 the bias which may be given by a theory. Jordan only 

 intended to decide experimentally whether the numerous 

 forms of the plant, as it occurs wild in different habitats, are 

 mere varieties or true species. He found that the different 

 forms do not pass into one another, and are in all cases re- 

 transformed after they have been altered by cultivation in a soil 

 different from that in which they usually grow, and he therefore 

 assumed that they were true species. All these experiments 

 therefore confirm the conclusion that external influences may 

 alter the individual, but that the changes produced are not 

 transmitted to the germs, and are never hereditary. 



Nageli indeed asserts that innate individual differences do 

 not exist in plants. The differences which we find, for instance, 

 between two beeches or oaks, are always, according to him, 

 modifications produced by the influence of varying local con- 

 ditions. But it is obvious that Nageli goes too far in this 

 respect, although it may be conceded that innate individual 



^ ' Sitzungsberichte der baierischen Akademie der Wissenschaften,' 

 vom 18 Nov. 1865. Compare also his ' Mechanisch-physiologische 

 Theorie der Abstammungslehre,' p. 102, etc. 



^ Jordan, ' Remarques sur le fait do I'existence en societe des especes 

 vegetales affines.' Lyon, 1873. 



