CONCLUDING REMARKS 22$ 



found in Egyptian tombs do not differ from the species existing to-day. 

 According to De Vries, a period of constancy may be followed by an 

 explosive tendency to mutate, whereby new species arise suddenly, while 

 the original species continues to exist. 



The most important fact, however, from our point of view is the per- 

 fect harmony between De Vries's theory of mutation and Mendel's ex- 

 periments on hybridization. The latter lead to the idea that hereditary 

 characteristics are transmitted by specific determinants in the sexual 

 cells, and that each characteristic must be represented by such a deter- 

 minant in the sexual cells. No two forms can have a closer resemblance 

 than corresponds to the difference between two determinants. If the 

 latter are comparable to the members of a series of compounds, e.g. of 

 alcohols, there is no more a transition possible between two species sepa- 

 rated by a difference in only one determinant than there is a transition 

 possible between the two neighboring alcohols of the same series. This 

 means that evolution must be discontinuous, as De Vries has actually 

 discovered it to be. 



Not all the new species which originate from (Enothera Lamarckiana 

 are capable of existence. The first mutation De Vries observed was a 

 form having pollen unfit for fertilization. It goes without saying that 

 such a form cannot exist in nature. But other forms can exist, and do 

 propagate side by side with (Enothera Lamarckiana. The limitation 

 for newly produced species is not the struggle for existence, but a 

 faulty construction. The idea that mutation is working in a definite 

 direction is a mere anthropomorphism, and like all anthropomorphisms 

 is in contradiction with the facts. 



