president s address. 7 1 7 



Addendum. — The De Vriesian Species. 



I have dealt so much with species from the nomenclature point 

 of view that it will be of interest to refer to another phase of the 

 species-question. I refer to the classical experiments of Prof. 

 Hugo De Vriese, undertaken with the view of throwing light upon 

 the formation of species. When in x\msterdam a couple of 

 years ago, Prof. De Vriese showed me very fully his interesting 

 experiments with plants of Oenothera^ and now I offer a digest 

 by my friend, Mr. E. Betche, of a recent paper,* giving an 

 account of these remarkable experiments and the theories arising 

 out of them. 



According to Darwin, the development of species takes place 

 gradually, by natural selection, but if we consider that species 

 have been proved to have remained in an unaltered state for 

 many centuries (weeds found in Egyptian mummies have been 

 found to be exactly identical with species growing at the present 

 day, after a lapse of about 4,000 years), the time required for the 

 development of the present forms of life is so enormous that 

 Darwin himself admits this to be a weak point in his theory. 



Kolliker advances another theory of the origin of species, 

 which he claims overcomes this difficulty; his theory is the 

 sudden development (mutation of the old investigators) of species, 

 as opposed to Darwin's gradual development. According to his 

 theory, the species lives for a period in a state of stability, then 

 the species gets old and seems to be no longer in complete 

 harmony witli the surrounding conditions; it then suddenly 

 breaks up into numerous forms — that is, a comparatively short 

 period of instability (mutation) follows the long period of 

 stability. The mother species suddenly develops a great number 

 of variations; some of these offspring-forms live only a few years 

 and die out again, others develop into new species and take 

 the place of the mother-form. With youthful freshness they 



* Hugo De Vriese, " Die Mutation und die Mutationsperioden bei der 

 Entstehung der Arten " Verhandl. Gesellsch. Deuts. Naturf. und Aerzte. 

 1901. 



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