52 PHYSIOLOGY CHAP. 



by the theory of De Vries. The majority of the new varieties 

 cultivated in the fields, orchards, and gardens, when not obtained 

 by hybridising, appear to have originated in such unexpected 

 mutations. 



These facts were illustrated and described, even before De Vries, 

 by Korschinski, who gave the phenomena the name of heter agenesis. 



De Vries in his famous experiments at the Botanical Garden of 

 Amsterdam saw several distinct species originate in a few years 

 from Oenothera Lamarckiana Oenothera gigas, 0. albida, 0. 

 rubrinervis, 0. nanella, etc., species which are said to give rise 

 on direct fertilisation to products of a constant character. This 

 would be the first experimental instance on record of neo-genesis 

 in species belonging to the higher organisms. Not all biologists, 

 however, are inclined to accept the conclusion of De Vries. Many 

 (among them Bateson, and Cuboni in Italy) maintain that the 

 so-called new species have no constant characters of descent, and 

 that the new forms observed by the illustrious botanist of 

 Amsterdam represent merely special cases of polyhybridism, in 

 which the dominant and recessive elements of the progenital 

 forms separate out according to Mendel's Law. In favour of this 

 supposition we have the fact that some of the pollen grains of 

 Oenothera Lamarckiana are deformed and sterile, as always occurs 

 with hybrids. 



If we admit that the mutations observed by De Vries are no 

 more than a return to the parent species, the fundamental basis 

 of his theory loses all evidential value. Further, it is undeniable 

 that many facts of systematic botany, and above all of palaeontol- 

 ogy, can be more readily interpreted on the generally accepted 

 theory of continuous variations. And lastly, it should be noted 

 that De Vries himself recognises that the all-essential point, i.e. 

 the internal causes of mutation, still remains an impenetrable 

 mystery to human investigation. 



Whatever the future of the different theories relating to the 

 mechanism by which the various living forms have developed one 

 from another, whatever the nature of the internal causes deter- 

 mining the formation of new species, it must never be forgotten 

 that the Law of Descent, i.e. the general Theory of Evolution, which 

 by means of Darwinism dominated the minds of scientific men 

 for half a century, has been marvellously fecund, and has incited a 

 vast series of researches, leading to the acquisition of new truths, 

 which without that theory might never have been gathered up. 

 It therefore remains the corner-stone of biological research ; even 

 more than as a hypothesis we are constrained to admit it as a 

 necessary postulate, because its negation would logically include 

 the negation of a unitary biological science. 



. From the foregoing observations on the vital activities common 



